K - right now if I put this tweet down: Closed Buy EURGBP 0.8552 for +65.0 pips, total for today +65.0 pips - The 150 people in my profile can see the tweet.
If I can put it down with a $ in front of the pair $EURUSD it will then post to Stocktwits, where I can broadcast it to the 80 000 people on Stocktwits. By doing that I change the profile to which I post, so instead of posting on mine, I post on theirs. Or I can add a $$ after the post to post to Stocktwits. Or I can add a # tag to tag the word #EURUSD to make it a keyword.
I don't know what the rest are, but the $ before and $$ after posts and the # are will help to get to get wider, relevant audiences.
I'm sure with time some extra symbols will come into it as well as twitter develops.