Mailbox for Birds-Squirrels-Union Square-NYC-Tree

Untapped Cities reader g1g1_nyc submitted this #DailyWhat of a “mailbox for birds” about 9 feet up on a tree in Union Square via Twitter. A closer photo by Magpie Musing shows that the front actually says U.S. Mail on it:

Not surprisingly, g1g1_nyc‘s tweet got some fun responses: @artwhkg asked “a penthouse for squirrels?” and @lalahon wrote, “Airmail??? hehehe.” Magpie’s photos were taken in 2007, but g1g1_nyc‘s just this past weekend, showing that this quirky mailbox has so far withstood the test of time. We’re still not sure what it’s really for though–any ideas?