Can you give us a sample of what your "billboard" looks like ? I have little to no imagination but can take a sample and then get my own ideas.I have... I was in the local Wal-mart and was wearing what I call my billboard shirt, which has everything we do on the back of it, and a guy came up to me and gave me his business card and asked if we can make him some hats and shirts, so we got the business.
I think it depends on what your designs are.How helpful is this in terms of advertising? I mean, have you ever gotten sales from random people by simply wearing your shirts?