Just stick a piece of duct tape to it and let the owners remove it. They will think the cat accidently stumbled upon the tape and not knowing any better rolled on top of it...
(plus if you do it symmetrically about its back it will look like a skunk with a pink stripe once the tape is removed)
Disclaimer: I am only kidding. My fiance and I have two cats, Guido and Yolanda... okay that's not their real names and she prefers that I don't call them by these names... shhhhhh...