There are too many methods to check.
There is
Echo: (Some strange occurrance)
Invis Spell: covered
Echoto: Message you only see as a player.
Send: Tell message.
Invis GM: They're in the room with you talking.
Then it also appears that they have a default script check message as well.
Echoto, Send, and Echos are all completely customizable. Were I a GM, that would be what I'd use.
-M
"We are the change that we've been screaming for."
- Strung Out, Mission Statement
If you receive rep signed -M, it's probably from me... or one of the other three people using the same signature. In the scheme of things though, do you really care?