The billboards seen during Baseball Bugs:
The outfield wall ad for "Mike Maltese, Ace Detective" refers to writer Michael Maltese.
The outfield wall ad for "Filboid Studge" refers to a fictional breakfast cereal mentioned in a short story by Saki.
The ad next to "Filboid Studge" is for "Culvert Gin" a take-off on "Calvert Gin."
The wall ads on the third base side are for "Manza Champagne", "Lausbub's Bread" and "Ross. Co. Finer Footwear for the Brats" named for animator Virgil Ross.
The ads on the left field wall are for Camuel's (a reference to Camel Cigarettes) and "Urbo."
Another outfield reading "Daltol" refers to animator Cal Dalton. A product named "Chi-Chi" is on a sign to the left.