»E 55th St and 2nd Ave

While running an errand, I saw this sign. I have always wondered what would happen if I did something like this, mistakenly dropping an un-addressed manila envelope or an interoffice mailer into a USPS box, or absent-mindedly putting a library book or my wallet instead of the letters into the slot. Other than patiently waiting near the box for the postie, the sign seems a sensible approach. When I passed by the box a half-hour later, the sign was gone.