Many abbreviations are context dependent.

In a canadian chat room, BC might mean British Columbia. In a guitar room, it might refer to BC Rich guitars. Etc.

Put the context that they were used in when you ask. Or ask right in the thread it was posted in originally.

Originally posted by E1:
Hi all!

Ne1, pls, help!
How should one decipher:
CLA?
TLA?
SHAMC
RHCP - red, hot... ok, got it...
RATM - rage against, yeah?
BC???!!!
AM???!!!!
Hmmm... last 2 got me stumped...

E-cue