Baseball uniforms for the New York Giants, New York Yankees and New York Mets have all used the interlocking letters “N” and “Y” for “New York.”
 
The New York Giants introduced the interlocking letters for uniforms in 1908.
 
The New York Yankees had interlocking letters in 1905, but there was only a partial overlap. The Yankees introduced the more common interlock for uniforms in 1909—one year after the New York Giants.
 
The New York Mets have interlocking letters on the team’s logo from 1962 until 1999. The interlocking letters are also on Mets baseball caps.
 
Baseball team uniforms with interlocking letters became popular after the Civil War. The Forest Citys (Cleveland, OH, 1869-1872) and the Forest Citys (Rockford, IL, 1871) both had uniforms with interlocking letters. The St. Louis Cardinals had interlocking “S” and “T” and “L” in 1900.
 
There are interlocking “NY” letters on the New York City Police Department medal of valor that was designed by the studios of Louis C. Tiffany in 1877. William Stephen Devery (1854-1919) was an NYPD chief in 1898 and a Yankees co-owner from 1903 until 1915. 
   
   
Logos-World
San Francisco Giants Logo
baseball club,sport,USA
Update: Jul 12, 2022
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1908
New York Giants logo 1908
The logo has a large classic Old English letter N in dark blue, indicating the location of the team – the city of New York.
 
Logos-World
New York Yankees Logo
baseball club,champion,USA
Update: Jul 12, 2022
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1905
New York Highlanders Logo 1905
The new interlocking “NY” letters appeared on the team fifth logo, but not in the way used today. The letter Y was overlapping the letter N. Besides, the color of the letters was changed to dark blue.
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1909 – 1912
New York Highlanders Logo 1909-1912
In 1909, the enduring logo as we know it made an appearance. It was the very first logo with stylized interlocking NY. According to the franchise owners’ version, the design of the most recognizable emblem in sports was created by Louis Tiffany.
 
Logos-World
New York Mets Logo
baseball club,NY,USA
Update: Jul 12, 2022
(...)
1962 – 1992
New York Mets Logo 1962-1992
The first logo, which eventually became the prototype for all subsequent ones, shows a white with an orange outline baseball, inside which is a view of Brooklyn. As mentioned earlier, each of the buildings is really in that order and corresponds to real structures. A white bridge is visible in the foreground. In the lower-left corner, you can see two small orange letters, “NY,” and in the very center, the word “Mets” in orange.
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1999 – today
New York Mets Logo 1999-Present
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Over the white bridge, on the dark blue figures of the essential skyscrapers from 5 districts of New York, the inscription “Mets” is displayed. The word is presented in the form of calligraphic handwriting. The interlacing of the letters “NY,” which was on the left, was deleted.
       
Baseball Researcher 
MONDAY, APRIL 12, 2010
That Famous Yankees Logo
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A close examination of the lower left edge of the medal reveals the words “TIFFANY & CO., N.Y.,” so it seems a safe bet the medal was designed and produced by the famous company, though it was almost assuredly not designed by Louis C. Tiffany himself.
   
Now let’s take a closer look at the portion of the medal that we are interested in the most:
   
Certainly the letters are centered and interlocking, like the Yankees logo. But is this unique? Actually, no.
   
New York (NY) Post
Yankees and NYPD ‘interlock’
By Gary Buiso
July 15, 2012 4:00am
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But it wasn’t until 1909 that the “NY” appeared on the uniform’s left sleeve and ball cap.
 
Francis said the prevailing theory is that Yankees owner William “Big Bill” Devery — a New York City police chief in 1898 — was behind it, though no direct link is known.
 
And interlocking letters were not uncommon on baseball uniforms. The “NY” was introduced on Yankees caps and sleeves a year after it appeared on New York Giants uniforms, noted Tony Morante, the Yankees director of stadium tours for the past 39 years.
 
A Tiffany’s spokesman said the logo was created at a time when meticulous records were not kept, so the company could not provide details about its relationship with the Yankees. The company now makes MLB’s commissioner’s trophy.
     
The History of Policing in the City of New York
The Creation & Evolution of the NYPD’s Medal of Honor? New Facts Revealed!
December 3, 2016
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Step 3: 1871 -The First Official Department Issued Medal
On April 5, 1871, the Police Department was the city’s first municipal department to officially award individual medals for valor.  The first medal for valor was awarded on August 17, 1871, to Patrolman (Ptl.) Bernard Tully of the Nineteenth Precinct (West Thirtieth St. Station-house) for the capture and arrest of a burglar.  Newspaper accounts indicated that Ptl. Tully was beaten “insensible, and his life was despaired of” by a “ruffian named Keeler” whom Ptl. Tully attempted to arrest.
 
The medal was described as being made of “silver or gold, either of which could be awarded at the discretion of the commissioners. The medals were presented on an ad hoc basis with no specific date, place, or event being mentioned. The design and shape differed throughout its thirteen years of existence which were between August 17, 1871 and January 21, 1884 and was presented a total of approximately sixteen times. The interlocking letters “NY” in this medal may appear familiar. The logo of the New York Yankees baseball team was influenced by this design.
       
Todd Radom Design
Interlocked, Intertwined, Interesting.
SEPTEMBER 19, 2017
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The New York Yankees cribbed their now famous interlocking “NY” from a New York City Police medal of valor that was designed by the studios of Louis C. Tiffany in 1877, more than two decades prior to the Bombers’ first usage. The Yankees (or Highlanders, as they were then known,) used this interlocking “NY” in 1905—it lasted but a single season.
   
The New York Giants introduced their own interlocking “NY” in 1909. It evolved over the years, right up until the Giants’ departure for San Francisco in 1958. The expansion New York Mets adopted it four years later and it still lives today, rendered in orange on a blue field, as opposed to black.
 
MLB.com—Yankees
NYPD & Tiffany: The story behind Yanks’ logo
February 4th, 2021
Bryan Hoch @BryanHoch
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According to an account published one day later in The New York Times, NYPD patrolman John McDowell was walking his beat in the early hours of Jan. 8, 1877, spotting a robbery inside a saloon at 315 Seventh Avenue. (The newspaper erroneously printed the officer’s surname as McDonnell.)
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McDowell recovered and was awarded the NYPD’s Medal of Valor, which prominently featured the interlocking “NY” symbol above a silver shield, depicting a woman placing a laurel wreath on a policeman’s head.
 
It was designed by Louis Tiffany of Tiffany & Co., and survives at the New York City Police Museum; the engraved back lauds McDowell “for bravery in pursuance of resolutions of the Board of Police of New York,” and is dated Jan. 12, 1877.
 
The baseball team arrived in 1903, the Highlanders playing their home games at Manhattan’s Hilltop Park while wearing an ornate “NY” across their chests. In 1909, the interlocking “NY” made its first appearance on the Highlanders’ uniform caps and left sleeves.
 
It is believed that the design was adopted by William “Big Bill” Devery, one of the club’s owners and a former chief in the NYPD.