It would appear that the hotels used to sell advertising on the backs of the hotel key holders. I have a bunch of key holders from the Plaza Hotel that have ads on the back for Harolds Club - like yours they are made of some kind of pre-plastic stuff. I also have two holders from the Plaza that are made of plastic and have ads for Harrah's - so I assume Harrah's must have out bid Harolds at some point. There are also a few holders that have the Harold's Club ad scratched off - guess Harrah's didn't provide enough holders to replace them all...