I just saw 'one less car' t-shirts for sale on the local craigs list-

i bet the lawyers will make you pay all of your proceeds to the organization if they do indeed have the rights to that phrase.

But it sucks, I agree. should have looked into it a little bit further.

My take on it, change your business name (you did register your business with the appropriate state and local entities, right?) and keep selling shirts promoting the anti vehicle theme. agree to send a portion of the profits from a shirt that you sell with the slogan 'one less car' on it to that organization that holds the trademark.