There used to be an old groan inducing joke that went like this. A worker who’s recently been fired shows up back at the workplace. The boss says, “I mailed you a letter to fire you; what are you doing back?” Employee says, “On the envelope it said, ‘Return in five days’, so here I am!”
I’m not sure if I ever saw this on an envelope, but I know I heard about it. I was probably eight when I heard the joke, and I didn’t need to have it explained, which shows it was something commonly enough understood in 1966 for that to be possible.
But what was the point of that? Presumably this instruction was intended for whoever handled the mail at a hotel or business office. If there was a forwarding address it was presumably moot, you were supposed to send the letter on.
Otherwise, though, you don’t normally leave a hotel for good without telling somebody at the front desk about it. If you’re gone, you’re gone, so why would they not send your letter back the day after you leave? On the other hand, if you leave but inform the staff that you will probably be back in two weeks, why would you not hold the mail until the guest returns?
Or was this more applicable to post office General Delivery (Message Left) windows? I can see how in the Great Depression there must have been an army of young itinerant workers getting a few days’ work where they could, and moving on when they couldn’t?