Interesting. I like the idea and have experienced first hand. I was in Ikea in Stockholm, Sweden (World's largest Ikea). I sat on the couch and a phone rang, brand new Sony Ericsson phone costing about $200 at that time. I answered the call. The guy couldn't speak English or was hysterical. I told him, I am giving it to Ikea folks, pick up from them and left. As I was exiting, Ikea lady showed him that I returned his phone and he was offering me monetary reward. I refused so don't know how much he was willing to give but I would like to know how much would you give. (Honestly, I got very offended by this gesture. I have very much Asian (Indian) looks and I felt like his actions are telling me that he was not expecting such action, i.e. returning a phone, from a person that looks like me, consider stereotypes..)
I have iPad (1st Gen), Verizon Motorola Xoom (1st Gen), HTC One X, Motorola Razr Droid. I would also like to out such sticker on my devices, just in case.
The guy probably was just trying to show his gratitude. I wouldn't accept, nor would I take offense. I'm Asian, too.