The AIM icon allows you to freely IM people who allow it. Some people have theirs set to not allow IM's from people who are not on their Buddy List.

But as a general rule, it's more courteous to PM someone and ask before you contact them on AIM. That way, they'll know it's you rather than some random stranger.

And for the record, my SN is Noise Electric and I welcome IM's from members of this board. So anyone here has my permission in advance to contact me on AIM if they so desire.

Cheers!