what about suspend/vacation?
That would like advertizing to the robbers they are free to break and enter.
Don't know, but since it is a much smaller group, I suspect that it is a continuation of the old systems with a printed or electronic list in the delivery vehicle.
In mobile home parks in Florida, the USPS puts a red dot on the mailboxes of the snowbirds when they are gone for the summer. They look like paper to me, though, as they get faded pretty quickly.