There is an understanding in user-interface work that an individual who clicks on something might further register the action if they experience some manner of feedback resulting from their action. There is also an understanding in user-interface work that succinct messages work best. These two understandings collide at the entrance to this apartment building.
I tried something different this time when I posted the photo. I put it up on Instagram, Facebook, and Twitter and asked people to provide their own captions. A bunch of folks piped up, and I liked these two responses in particular: jdginstagramz (via Instagram): “Self-Captioned.” And Paul Lamere (via Twitter): “TCP doorbell.”