There's an opportunity here if you pursue it. Turn it around on them.
Quote them a price with and without them getting a set of digital copies of their "logo" and then tell them that everytime they do this kind of thing they are getting charged to reinvent their logo ... whether or not the printer or the T-Shirt guy or the sign company or whoever tells them so ... they are paying extra.
Quite a few of them end up agreeing and paying a setup fee in excess of what would get built into their price for the signs they want.