'Sorry Can't Talk'
'SCT' is a polite but direct way to be used in online chat and, if deemed necessary, in public. Usually used when an online chat program like Skype, MSN, Facebook signs you on without noticing and you need to communicate to friends that you dont want to be rude but dont want to, or cannot talk, when they suddenly, and often unexpectedly begin talking to you.
*Sound indicator that someone is chatting to you*
Facebook chat friend: Ay bro! Long time no talk!
Facebook chat friend: How you been!?
Facebook chat friend: Oh, not a problem man spk soon.