“Welcome to Texas. Beware of the Bull”

“Welcome to Texas. Beware of the Bull” has been quoted (since the 1950s) as being a sign near the Oklahoma border.
   
 
8 April 1958, Jefferson (Iowa) Bee, pg. 16, col. 2:
A recent visitor in Texas said he noted a sign reading “Welcome to Texas” as he went across the state line. But then he also noted a sign over on the fence that read: “Beware of the Bull.”
     
10 March 1971, Charleston (WV) Gazette, pg. 13, col. 5:
TOURIST reports he had always heard a lot about how Texans brag but he dismissed most of it as just rumor until he recently made a trip to Dallas. He was driving, he said, and as he crossed the border he saw a large sign that read: “You Are Now In Texas.” Just a few feet down the highway, he reports, there was another sign. This one read: “Beware of Bull.”
   
1001 Greatest Things Ever Said About Texas
edited by Donna Ingham
Guilford, CT: The Lyons Press
2006
Pg. 89:
You are now entering Texas.
Beware of Bull!
—sign on a ranch fence on the Texas side of the Red River bordering Oklahoma.