I think it somewhat depends on how well known you are and how much you believe in advertising.
If the shop is going to market it as "a block specially designed by you" as an enticement, then they are using you for their advertising. If the people in your area don't know much about you, then getting your name on it as well is pretty good free advertising that you are getting from the shop.
I'd probably be willing to give away the block in return for the advertising/name recognition.