Being that I'm a graphic designer and love photography making signature cards was inevitable. I do not toss them in caches in the place of signing a log, nor do I trade swag for them. In fact most of my sig cards highlight other caches that I really enjoyed. On the back I give the cache number and name.
In the end I do it for my own enjoyment. I love photography, caching, and design.
It matters little to me if they end up in the trash or someones collection, I had fun making them.