I use BTC for Bitcoin and BCT for Bitcointalk. This lead to some ambiguity when programming variables. BTT might stand out easier but the syllables of BitCoinTalk start with BCT. 
it is a standard that when creating an abbreviation you pick the first letter of the syllable newbies here will ask why BTT but if it is BCT they will understand why BCTbecause of B it C oin T alk