Commissioned Art on Calling Cards?

[mandyseley.livejournal.com]

I want to make a run of calling cards for myself, and showcase some of my artwork on the back. Some of my best work is commissioned work from drawing other people's roleplay characters and fursonas.

I understand that I own the rights to the images (and my customers get a little explanation of that before I work with them, it's right in my TOS) and that it's unlikely that they've registered a trademark for their D&D character or fursona, but would it be in poor taste to use the images on my calling cards to promote myself?

I've sent emails asking my customers for their permission before I order the cards, but are there any legal concerns I should be aware of?

I of course would NOT be selling the cards, just handing them out for free when I want to quickly give my contact information and a little sample of my work to a potential customer/friend/networking connection.