How to properly credit sources on Twitter, via the Business Insider:
MT = Modified tweet. This means the tweet you’re looking at is a paraphrase of a tweet originally written by someone else.
RT = Retweet. The tweet you’re looking at was forwarded to you by another user.
PRT = Partial retweet. The tweet you’re looking at is the truncated version of someone else’s tweet.
HT = Hat tip. This is a way of attributing a link to another Twitter user.
CC = Carbon-copy. Works the same way as email.

MG Seigler, in a follow-up piece to the tweet below that made the copy-paste and rewrite natives rather restive:
@marcoarment I used to love to plant one really weird bit of random information (sometimes even false) into stories to catch the rewrites.
— MG Siegler (@parislemon) July 5, 2012