We had something similar in molecular biology, where the class was divided into ten different groups each of several students, with random group quizzes once a week. We'd share a grade so ultimately a signature was necessary to receive credit for participation. Went smoothly for the first several weeks, but then the professor got the paper back with eight signatures even though there were clearly just seven students. He called them out to the class, failing both the girl that forged the signature and the girl that was absent. I love justice.
I've noticed a few of my own students blatantly copying off of each other before lab in their homework, but as a TA I don't want to have to deal with all the hierarchy in reporting it and anything actually happening, not to mention that what they cheat on constitutes less than 10% of the total lab grade, so I just keep myself happy knowing that the students that cheat are failing their exams. Officially it's all "zero tolerance" and shit but you'd have to be caught cheating on an exam by a professor for anything to really happen, it seems. I wish that I could just give the offenders easy zeroes and tell them to fuck off if they had a problem with it. I'd probably be more understanding if I had friends that helped me in undergrad, however.
EDIT: Actually, in an intro biology class with 250 students there was a similar trap set up. Kids would skip class and leave their attendance clickers/remotes with a friend so that they would appear present, but on one day towards the end of the semester, the professor put the class on lockdown and had proctors walk around collecting signatures from each student personally. Those that were supposedly there by remote but not actually had a penalty that amounted to losing a full letter grade. 30-40 pre-med assholes getting their GPAs fucked in what should be an easy A class, absolutely beautiful.