Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
I would suggest a sweatshirt instead of a shirt, since keeping warm is a huge concern for the homeless this time of year (which is why you see all the coat drives).
It would be more efficient, but I like the idea of decentralizing the project. I think it would be cool if there was a single design, but they were printed and distributed locally. This may be thinking too big picture or down the road, but something like this, if well documented and publicized, could very easily become a "thing" and attract outside donations that made it possible to do on a larger scale down the road. Would be amazing publicity for this community as well (if that's desired at all). Just a thought.