Traditionally you had a catch-phrase, a bit of comic business (Leonard Rossiter spilling his Cinzano on Joan Collins) or an unmistakable sound (brass bands for Hovis). Increasingly, you had a bit of mystification borrowed from art movies and new software.
For the past 10 years major commercials have been heavily PR-led. Why spend pounds 10m in paid-for media if pounds 60,000 of PR can have the same effect?
But the new Vanish commercials propose a more modern, self-referential method: assume that your advertising is famous already and devote your slots entirely to those supermarket car-park conversations of the "you know the bit when ..." and "that's the music from X, I've been singing it all day" variety.
Thus these two blokes in a changing room, one towelled round the waist, one completely covered. They talk serious man's talk: "The Vanish stain removal sequence ... fantastic ... shocking really" and the real clincher: "Bob and I were talking about that the other day".
Another 10 seconds opens on urban desolation - a flyover from below, a plastic bag blowing across the road - with a snatch of conversation from a passing taxi. A woman says, "I recognise that - it's the Vanish tablets." The driver says, "You're the fourth person today".
There are at least two more - waitresses talking at a reception; a man on bonfire duty in the garden called in by his wife ("Quick, the Vanish ad is on") following this Mass Observation route.
Every creative team wants to magic the banal into a living demo of mass cultural theory. But the most surreal thing of all, I suspect, is that most viewers know how it's done, too.