I'm a visual kinda guy, so I start the recognising project by that through looking at the avatar.
I then glance up to title and username and then look below that to the postcount. If those match what I expect them to be the "alarmbells" stay off. During avatar-switches or new avatars, title or username changes I'm still quiet able to identify the indivuduals in this way.
If something doesn't add up the "alarmbells" start ringing and a glance at the signature, posting style, location and join-date usually does the trick. If that fails I'll check previous posts and threads started by that person. There my possibilities as a regular member sort of end, but my Mod Superpowers have more identifying possibilities that I can't talk about...