Syntax:  Alone shows your current message. 
          .set entermsg <message>        lets you put a message in.
          .set entermsg [clear|-c|none]  resets to default

Results:  When you walk in a room, instead of "<user> walks in." it 
          shows "<user> <your entermsg>"
          This message is saved to disk between logins.

See also: go, set_exitmsg