Thanks for the help guys. I did just install AE's uhh... "see who uses multiple logins using a different cookie than VB" mod. Can't remember what it's called. Anyway, it is supposed to leave a cookie that's not cleared by logging out. This almost does what I want, but only if the person logs in again under a different account. I just want to see when someone logs out but continues to lurk from the same computer. It can't be too far off from this mod.
Aha, found it:
https://vborg.vbsupport.ru/showthread.php?t=125871
Also, while I have some attention, I'm looking for a way to display various types of ads/things on specific threads I select. Is that just done with a template IF statement? IF so, does that clutter things up or slow down execution much? Let's say I have a couple threads that get a lot of views but mostly from lurkers/guests/likely to bounce search engine traffic. I want to put Google ads along the side and/or top/bottom/whatever. Do I just put "if blah blah = showthread?t=22342" type of statement into the showthread template? Or is there a more elegant way to do this, maybe with a ACP control panel for it all, so I don't have to go digging thru templates each time?
Thanks again.