One way to test the waters on this is to provide a digital file of a sign (in a universal high-res, print-ready PDF format), with maybe a few links to on-line sign makers. Folks interested could download the file and order their own signs, in whatever size or material or quality level they prefer (and want to pay for). The PDF format can be resolution-independent (vector format) to accommodate any size without compromising print quality. And if linking to print shops violates the TFP website rules, then perhaps just a hint on what to google to find your own print shop would suffice...
If there was interest, TFP could provide a variety of files, of different designs and content (sayings). Then, if there was a lot of interest, TFP could start selling the signs themselves.
If one was to send the file to a screen printer that could get the design onto a speedo, so be it...