If it was me, I'd probably drop him an e-mail stating that you keep a regular eye on his site and noticed that he had indeed used your design, referencing your e-mail and his reply.
Leave it quite vague as your intentions and see if you get any kind of response - you never know, he might have lost your e-mail details and had every intention of thanking you or sending you a freebie!
Leave it quite vague as your intentions and see if you get any kind of response - you never know, he might have lost your e-mail details and had every intention of thanking you or sending you a freebie!