81. It dawns on Lois in "Top Copy" that Diana showed up in the newsroom with the weird device that Superman shorted because it was a tracker for Superman. She decides that she wants to figure out what Clark does when he runs away to return a video or go to a forgotten dentist appointment. So as they are going back in at the end to finnish their chess game she kisses him with her lipstick that has a tracer in it.
Since Lois is only remotely tracking him he has no clue. The next day when Superman goes to help avert a plane crash in Mexico Lois notices Clark moving very fast and realizes that Diana was right and Clark really is Superman.
