Would assume it's much like same as EWR -- gate keeper at the entrance to the "pen" asking if you're 1K/Polaris

Smaller stations that are big enough to have a specifically signed 1K/Polaris lane aren't actively enforced (in my experience) but also don't really have compliance issues -- usually those who are there and "don't belong" have been waved over by an agent.

I've never been inconvenienced by it and at most stations it's nothing special anyway -- if it got you, for example, actual agent to check you in instead of just another kiosk with a contracted bag-tagger I might be more uppity about it but that is exceptionally uncommon -- BOS being the only place I saw it somewhat consistently -- but it;s also been a couple years since I've been to BOS and I imagine things my have changed. In EWR, for example, the gatekeeper is more of an annoyance (IMO) than anything else... you just have to mumble something vaguely affirmative to their "1K? Polaris? First?" interrogation and they shrug in the general direction of the kiosks. It would be a better experience if that resource were used to tag bags and assist passengers with problems since EWR is consistently my longest wait between "tag printed" and "bag on conveyor"