Make it black, or very dark grey and make sure the shirt is "Made in the USA" and I'm in. I can even contribute a photo is desired. I wouldn't even mind something like: "Taylor Guitar's - Made in the USA," but that might alienate owner's of 100 and 200 series guitars, so that's out.
How about this: on the back the profile of a guitar on the right (in relief) cropped right at the edge of the fretboard, and on the left from top to bottom and in alignment with the frets, the series 100, 200,... 900. On the bottom it says, "Take your pick!" using a morphed pick as an exclamation point. This should be underlined with the url. It would be an intersting play on words. On the front, the pocket can say UTFG with the url underneath it. The whole thing can be done in black and white.
(I'm in marketing and product management)
Jim