Theft of promo material designs - How do you deal?

[ForrestBlack]

Sometimes sponsors don't have quite the right materials to sell best to certain audiences, so I like to design promo materials, banners and such, with sponsor provided content and logos and all that which appeal to my various traffic sites. But a fair amount of the time, I've been finding that the banners and such that I design for my traffic sites tend to be kind of stolen and used by other people on their sites.

On the one hand, it is sponsor provided content, so it's not as bad as if it was totally original, but on the otherhand I worked hard on the design and other people should have to work just as hard if they want to make sales.

The problem is that every time I've ever tried the option of sending another site owner a note asking that they not use my design, they get kinda pissy and decide they have a problem with me forever, which seems kind of unreasonable.

For those of you who create your own designs, for galleries, banners, whatever, how do you deal with it when other people take liberties with them?

Forrest-

[ForrestBlack]

Bump for the night time folks?