This post has inspired an ongoing experiment.
Normally I have PMs restricted to my friends list. Over this past weekend, I changed it to allow anybody, to see what happens.
For several days, I was logged on only briefly. No mentions in topics, no PMs.
Tuesday, I was logged on for 3 1/2 hours. 8 minutes after logging on, I was listed in the topic of a room as one of the high tippers. This is not a particularly high ranked model - between #100 and #200, camscore around 5000. First page, but not first row. 14 minutes later (gotta love timestamps in chat archives), I got a PM from a model I had had no previous contact with. No more after that, in spite of still being high tip in the topic for the rest of the time. Also, my whole userid wasn't listed in the topic, just a shortened version of it.
I'm leaving the ID logged in for 9 or 10 hours today to see what happens.