OK, let's find a referent. Figure 1 presents a picture of a referent. The referent here is snowboarding. Or to put it in Saussure's terms, the referent is what gets your knee torn up.
Unless, of course, your "in control." Speaking of taking risks, yet being in control (what a conceit), have you heard about trojan condoms? Boom, we are into a different referent system: the referent of condoms and sexual intercourse.
In the space of the ad, the picture of a skateboarder functions as a signifier. The crucial exchange in the ad between the two different meanings of being "in control" permits the skateboarder to become a signifier of Trojan. The signifier has jumped ship to join another signified.
Take that moment when the referent is eclipsed by the signifier and multiply it by all the ads you have ever seen, and you...well, you get the picture.