I'd proudly and happily rock these shirts in public:
http://www.hellotux.com/Category_Polo.php (I'd especially rock the Linux Mint ones)
I will at least say that I'd be rocking it because I have a genuine interest in Linux and the Linux community, rather than for "Hipster Faux Nerd" reasons or whatever kids, teens and twenty-somethings/20-somethings these days do.
This is the kind of stuff you would probably rarely see people wear in public. They would probably be too embarrassed to do so. But no sir! Not this Linux fanboy!
ROCK ON! \m/