How do you inform Gala guest not to take the centerpieces?

You got some really good answers. I just had to say that it truly appalls me that people do actually do this. Where they come off thinking it is OK just never seems to surprise me!!! A centerpiece is not a "parting gift". I would as others say, at the end of the evening, make an announcement about the gifts you are giving about but make an annoucement how the centerpieces are on "loan" and from whom in case someone would want to use them in the future. I would also put a business card from the propriter in front of the crystal candle holders so they can contact them if they choose. AND...as an added protection I would have someone at the door watching because people do have STICKY fingers and even though you do everything in your power to let them know they are not for the taking SOMEONE is bound to try to take one!!! Good luck, enjoy your Gala!!! You sound like a wonderful host!!!