Tell us where they're located in the comments. Update: The mural's located in the Space Gallery window above the Hemlock Tavern (Polk and Sutter). Go check out the kittens before they get painted over or something. Thanks to Commenters jaredf, thetens, and Generik11 for the help!
Update II: SFist walked by Space Gallery this evening, and the kittens weren't there!