Alright, now this is an old concern (which has been re-raised many times, but most recently today) which I don't think we've done well to address in the past.
Basically, a newbie looks in the chatroom (or on the forum) and sees language like GM-Re. Now, the question is, what the hell does this mean?
Somebody who's been around for a long time, like me (and has played their fair share of Sonic Heroes, like me >_>) will recognise it without too much trouble. But in the interest of helping the new guys out, here's how it works:
Everything before the - symbol is an abbreviation of the level name (in this case, Grand Metropolis in Sonic Heroes). In cases where more than one level has the same abbreviation (eg. Metal Harbor and Meteor Herd) an additional letter can be added to remove the ambiguity, ie. MHa and MHe.
The first letter after the - symbol indicates the character (in this case, Team Rose). This works well enough, with one exception: in Sonic 06, all the characters start with S (Sonic, Shadow, Silver) and must again have an additional letter to remove ambiguity, but that messes with the third and final part a little.
As part of a legacy from the days when TSC was only about times, the default mode of thinking when you state a level-character combination is that it is being played for time. To indicate something else, add r for rings, s for scores (and in this case, Extra, you can use either e or x and the meaning is understood). As you can see, in the Sonic 06 instance above this presents a problem because you end up with something like FC-Sir. In this case it is advisable to put the r in brackets.
Finally, if two levels in separate games share an abbreviation (the obvious one being Casino Night/Carnival Night) then just add the game name at the end in brackets.
So, a couple of examples:
WC1 - Wild Canyon, mission 1, time, Sonic Adventure 2
DE-K - Death Egg, Knuckles, time, Sonic 2 (note Sonic 2 is implied - Sonic & Knuckles Death Egg has two acts)
TB2-Cs - Techno Base 2, Cream, score, Sonic Advance 2
CN2-S (S3) - Carnival Night 2, Sonic, time, Sonic 3
FiF-De - Final Fortress, Dark, extra, Sonic Heroes (to distinguish from Frog Forest)
TODO: list of level abbreviations