It's from the play "Pyramus and Thisbe" inside the play "Midsummer Night's Dream", about "two lovers in the city of Babylon who occupy connected houses, forbidden by their parents to be wed, because of their parents' rivalry." (Wikipedia) One of the plot points is that Pyramus and Thisbe meet at opposite sides of a wall nightly to talk to each other.
For the play inside the play, the actors couldn't get a wall, so they had one of their troupe play Wall itself. When Pyramus says the words above, he's searching for a hole in the wall to see through to gaze upon his love. The actor playing Wall obliges by making an "ok" hand gesture for Pyramus to see through.