There is some watch code here so you can keep an eye out for your friends and be alerted when they log in and log off. You have a watch list of people you are interested in, when someone on that list logs on/off you are informed. Use the following to manage your watch list.
+watch/add <name>
+watch/rem <name>
If you want to conceal your login/logout from someone, that can be arranged as well, as as well as a watch list you have a hide list, a list of players you are concealing yourself from. You can manage that list with the following commands.
+watch/hide <name>
+watch/unhide <name>
And you can get a list of who you are watching for, who you are hiding from, and who is watching for you, with the following :-
+watch
Finally you can just hide from everybody, opting out of the whole system in effect.
+watch/hidefromall
+watch/unhidefromall