I don't think the mods even remotely care if I sign up with a dupe and being the gigantic manchild that I am, that hurts my ego enough not to never sign up with a dupe.
Generally speaking, given how huge the forum is, the mods (or at least most mods at the very least) don't remotely care if anyone signs up with a dupe account in and of itself. We don't have an automated system to detect it, and given the sheer volume of registrants it would be a colossal waste of time to randomly check junior members for past bans. What does happen, however, is that often times someone pops up and they're not doing anything flagrantly wrong to warrant the obvious ban, but something about what they're doing seems mildly familiar and somewhat problematic. And they just seem to know more about the forum than the typical junior, or they seem to be posting with just the sort of devil may care attitude that comes from knowing "who gives a shit about getting banned at this stupid place; I can just register another account if I really want to post there again anyway."
So more often than not, the confirmation that someone used to be Previous Banned User #15335 doesn't in and of itself warrant the ban, but it's that knowledge plus the fact that someone even bothered to check up on the user to begin with that basically settles what would have otherwise been a coin flip to decide whether they stay or not. To put it another way, nobody ever thinks "wow, this new junior is a really great poster. I wonder if they're a reformed, previously banned member."
