Usually in larger stations and it is really infrequent. It's usually a bunch of patrol cops with a plastic folding table and they set it up in the station outsi

Usually in larger stations and it is really infrequent. It's usually a bunch of patrol cops with a plastic folding table and they set it up in the station outside the turnstiles. They'll "randomly" select people and check their bags. I've seen them in Queens (Roosevelt/74th) and other random stations.