If your store is like ours, there are windows you view the cats through? Couldn't you post a sign on one of those? Not a big one.. Something simple and small...."Be a Dear and Be a Volunteer"... Could put sayings like that on a heart shaped cut outs or cat cut outs and stick to the glass. "Hands Wanted! I need petting!" on a hand cut out...? Just throwing a few ideas at you...