I was just looking at a subpoena that concludes, "Fail not at your peril."
Evidently, subpoenas used to always say that.
I can guess what it means, but it seems like a strange bit of usage to me.
Some guy named Steve posted this:
"Back in the good old days, when courts were allowed to inflict cruel and unusual punishment willy nilly, a subpoena concluded with the legend: 'HEREIN FAIL NOT AT YOUR PERIL.' The recipient was left to imagine what might happen to one who ignored such an order from a court. Whatever that consequence might be, it was sure to be painful, hence the name 'sub poena' meaning 'under pain.'"