[AnonChick]

I don't think it needs to be turned into a rule. It's not a rule anywhere else really, it's more a matter of courtesy vs. selfishness, and the consequences of natural order.

Basically - they put up a sign reminding everyone that the management will not be held responsible for the seats, or anything left on the seats, if those seats are abandoned by their "reservers."

And then, the people who want to actually SIT in them - do so.

And then, the reservers return, find "their" seats are occupied, and they can't do diddly about it and have to suck it up and find somewhere else to sit.

Because the management has already warned them that they reserve seats at their own risk, there's nothing more to do about it.