For anyone who objects to tags I have heard the average life of a business card is about 10 seconds. Why not put a piece of blue painter's tape on the back of your business card? If your customer does not want the tag they can throw it away with the card. If they want the tag they can peel it off the painters tape and put it on there racket or anywhere else they make want to stick it. Painter's tape does not stick well on either side.
If they peel the painter's tape off and trim it up it is real easy to get off the racket too.
I have the ability to drive people crazy, not sure if I was born with it or I learned it but I'm damn good at it.