“Welcome to our ‘ool’. Notice there’s no ‘P’ in it. Let’s keep it that way”

“Welcome to our ‘ool’. Notice there’s no ‘P’ in it. Let’s keep it that way” is a jocular saying (against “pee” in the pool) that has been printed on many images. The “ool” pool signs have been cited in print since at least 1976.
 
   
5 September 1976, Chicago (IL) Tribune, “A farewell to charms: Atlantic City, 1976,” Magazine sec., pg. 15, col. 2:
... and souvenir stalls that sell posters of “The Fonz” and the Atlantic Ocean (complete with the message, “Welcome to our Ool. There’s no P in it. Please Keep It That Way”).
   
23 July 1977, Indianapolis (IN) News, “Did You Notice?.” pg. 13, col. 1:
Sign on backyard pool: “Welcome to our OOL. You’ll notice it has no P.”
 
30 January 1983, Minneapolis (MN) Tribune, “Hollywood leaves TV critic flushed with wonder” by Nick Coleman,
We wandered around the grounds at the house that breasts built, waiting for the boy himself, Playboy chairman Hugh Hefner, to show up. A sign on the entry of the grotto behind the mansion where Hefner lolls about in the Jacuzzi with his playmates told much about the tastes of the man: “Welcome to our Ool,” it said. “Notice: there is no P in it. Keep it that way.”
   
Google Books
Singapore English in a nutshell:
An alphabetical description of its features
By Adam Brown
Singapore: Federal Publications
1999
Pg. ?:
A local hotel has this notice by its swimming pool:
 
Welcome to our ool. You will notice there is no P in it. Please keep it that way.
   
Google Books
Get Thee to a Punnery:
An Anthology of Intentional Assaults Upon the English Language
By Richard Lederer
Layton, UT: Gibbs Smith
2006
Pg. ?:
At a swimming pool: Welcome to our ool. You notice there’s no P in it. Please keep it that way.
   
Google Books
Crossing the Divide:
A Family Adventure Along the Continental Divide
By Richard Mallery
eBookIt.com
2014
Pg. ?:
Next to the swimming pool there was a sign: “Welcome to our “ool”. As you can see there is no “P” in our “ool” so let’s keep it that way!”
 
Twitter
lizzie
‏@lizzie_b7
This is way better than the “Welcome to our ‘ool’. Notice there’s no ‘p’ in it. Let’s keep it that way” sign.
8:42 PM - 17 Jul 2018