LONDON — One by one, the swimmers emerge poolside from behind a wall, making their way to the starting blocks at the Olympic aquatics center in a procession that combines the drama of sport, the staging of prime-time TV and the posturing of a fashion-show catwalk. This conspicuous scene, playing out many times a day at the London Games, has also become an international advertising bonanza for a product not usually associated with water sports: headphones.

Some swimmers dance or showboat as they walk across the pool’s deck. Most acknowledge the crowd with a wave. But many more strut out coolly toward their lanes wearing headphones. These are rather massive headgear that, when twinned with mirrored goggles and the pounding beats of artists like Lil Wayne and Cash Money Millionaires, shut out all outside stimuli in the pursuit of perfect prerace concentration.

Olympic officials are famously relentless in snuffing out any appearance of an unofficial sponsor at the Games; athletes are prohibited from posting Twitter messages about their individual sponsors, and even the brand logo on toilet-paper dispensers is covered with black tape lest anyone think Bay West is an official partner of the London Games. But the headphones on display at the aquatics center have so far evaded the brand police, surely to the delight of the companies that did not have to pay for their logos to be seen by millions of viewers around the world.

“It has enormous value,” Mike Lescarbeau, chief executive of Carmichael Lynch, an advertising firm in Minneapolis, said about Olympic athletes being seen wearing the headphones. “It’s kind of the new world order. You are doing placement in real time.”