1337 Girl's T-Shirt

Leet or Leetspeak is simply a way of writing by replacing letters with numbers or ASCII symbols and frequently includes intentional misspellings. It began as a form of encrypted communication among hackers to circumvent text filters on bulletin board systems (BBS) where a user with "elite" status could access files regular users could not. It has since evolved and is now widely used in gaming and Internet forums, often for expressive insults and proclamation.

1337, L33t, 31337, etc are phonetic derivatives of the word "elite". It refers to someone's superior ability or status, the opposite of which being "n00b", someone displaying inept qualities.

Elite is also a game developed by David Braben and Ian Bell. It was a revolutionary combination of wireframe 3D graphics, trading and space combat. Originally published by Acornsoft in 1984 for the BBC Micro, it was subsequently ported over to many platforms including the Amstrad CPC, ZX Spectrum and C64 by publisher Firebird.

Bringing the two together, this is a design inspired by the game's golden logo for those who like to pwn.