Papers
If you asked Mr. Hades, Hadestown didn't ask much of its citizens. All you had to do was buy a ticket in, sign your papers, and you'd be given a job, room and board. Nice and easy.
If you asked a worker, they'd agree it wasn't hard. The conditions were all there in black and red ink, nice and official, and all you had to do was sign your name. You barely had to read your papers, since time was money and could be better spent on the line. If you read closely and signed anyway, well, that was on you.
There was something binding to those papers, but what it was, Mr. Hades didn't say, and the workers didn't know. Maybe it was your name that you once had but let slip away, buried in words and ink and promises. Maybe it was the act of signing, in itself, to show you were willing to trade your life for security.
Regardless, every worker had their papers signed and stamped, and anyone that didn't clearly wasn't from Hadestown. Orpheus, Hades vowed, would learn it the hard way.