Intrinsica, on 15 February 2013 - 15:20, said:
Well that is odd then. Pretty much everywhere else they would have used a dash...
It's just a convention. Like in most places to refer to someone in a message, I may do something like
"Intrinsica: It's just a convention"
On twitter I would do
"@Intrinsica It's just a convention"
I guess by using a character not usually used in the messages themselves, it allows easier automated analysis of tweets