Way back in 2001, London.pm organised a series of tshirts. As Dave Cross explained:
They all have a large "Programming Republic of London" logo on the back and one of a series of small "fictional" PM group logos on the front. I'm currently wearing my Sunnydale.pm shirt, but we also have Rivendell.pm, Tatooine.pm, ZZ9PluralZAlpha.pm[1] and Anhk-Morpork.pm (the last is for those strange people who can't see that Terry Pratchett is an unfunny, fifth-rate Douglas Adams wannabe).
Also, see the images as Simon Wistow explains:
Yes, the rumours are true. After epic battles with every t-shirt printer in london the official Winter Season London.pm t-shirts are finally ready.
Embarassingly we left out our favourite fictional Perl Monger group. However, it was, how shall I say, quite a lot of organising and quite tiring to ship tshirts around London and the world. Luckily, now we live in the future and I can outsource all that, so behold the official London.pm Gallifrey.pm tshirt.
It's being sold at cost and you can wear one at all fashionable geek gatherings. Enjoy!
Update: now with a women's tshirt and also available in the USA: men's, women's.
Embarassingly we left out our favourite fictional Perl Monger group.
I'm pretty sure it was discussed. But remember that back in 2001 Gallifrey was even more obscure than zz9PluralzAlpha. So in the end we decided against it.
Of course, Gallifrey.pm t-shirts will be even more in demand now - what with the planet being destroyed in the Time War.