Andersp:
If I have made quite a few moves on a game and my opponent is one who always moves if they see me moving, all I have to do is say good night in the message. I have done this for years. You generally get to know your opponents if you play the same people over and over again I find that if they are going to leave they will normally tell me goodnight. Other opponents just make one move and I know they are not going to move again.