In the last scene of "The Blind Banker" where Sherlock and John are having breakfast, John looks out the window and sees a female street artist spray painting an eye onto a box.

I've been wondering what the significance of the eye is because all of the details of the show are really important.

Maybe it symbolizes Morirarty's omniscient presence? Maybe it is a symbol of Sherlock's perception and clarity? Maybe it's a threat? A warning?

What could the graffiti eye mean?