Development of Creative Commons licenses

[Sigmascape1 AT cs.com]

Hello,

Quick question for you guys. I am interested in designing some t-shirts that 
promote a certain type of cc-related cause. On the front, the URL is shown, 
on the back, I'd like to place either a CC Attribution logo or possibly a 
Public Domain logo. So, first, is it even conceivable, and, two, if it is, do 
I need to sign some sort of trademark usage license? The sales of the 
t-shirts goes towards the cc-friendly cause, but is in no way officially 
endorsed by cc.

Thanks!!!

Mitch