This is quite obviously a hatch to an underground station. If he chooses to open it, I certainly hope that he is a good typist and has some time on his hands.
I have to agree with Scotchdrnkr on this one. Hard to argue with money (or something readily exchanged for it) falling from the sky, and looks like he has some free advertising to boot!
I am as well-read as the next guy but I'm at a loss for what the subtle literary joke is here. Perhaps it's only comprehensible to those who've partaken in the large quantities of Star Trek 'literature' that is available at their local discount bookseller?