From Albert’s…..Button could be for the Post Office, a quick search shows POD as the following.
POD Post Office Department
POD Post Office Delivery
All that said, I didn't find an example with just POD, everything I found also has a letter carrier on the button.
I believe that may be an old sliding/pocket door mortise lock, but instead of a key (as below), it had a small privacy knob.The bigger object looks like an end for a roll up blind.