Notice on door
If you find a notice or notification on the door, do not worry.
If the notice is from the Water Department, and they are saying something like "access denied" or that they were trying to read the water meter but could not, don't fret. The water department is looking for a meter for 3517, which doesn't exist. You can remove the notice and throw it away.
If there is a notice from FedEx, UPS or other shipping company, and there is a contact person named on the notice, you can leave it right there or try to find the person mentioned. If you feel you must email someone and you can't figure out who to contact, email email@example.com
If you want to post it to Google Groups or Slack, then knock yourself out.
That said, most people getting things delivered to PS1 know the score and these things are ordinary parts of the process. They may have a tracking number and know about it already.