If you used it and checked the Meta board you would find that's it's an SMF easter egg. When the post count reaches 1337, it is replaced by the word 'leet'. You can google 1337 to read more about it but a simple way of understanding it is that it's a language, where English letters are replaced by ASCII symbols.
i.e. leet = 1337, theymos = 7|^.3'/|\/|05
as examples
/thread
Thanks for that. I'm learning and will make sure I use that search tool in the future.
Locking this thread now. Apologies for this redundant thread. Googling "bitcointalk leet" I now see this has been addressed in multiple threads in the past.