[telemachos]

I think it's an IRC-ism since there you can type

    /me nods

And the "/me" token will be replaced by your username and the whole "action" will be a different style (font/color/what-have-you) on some clients.

[moeffju]

The same command works on Skype and does what one would expect. It's just not really advertised. Try typing /help in a Skype chat window.