It is essentially a swap-meet. Passersby stop, study and if they like what they see offer a trade for a pin they've already got. It can come down to the ability to talk a trader into a potential bargain.
Mother and daughter Carol and Krystal Lord have come from Delta, British Colombia. Carol is a florist; Krystal an artist, who has a leaning towards abstract work and cartoons.
It's their first visit to London, and the second Olympics, after their own Winter Games in Vancouver two years ago.
"It's fun and you make friends," Krystal said.
And her artist's eye explains part of the reason they're here - "I like the designs of the pins."
Her mother explained how the system works. You are legally not allowed to buy or sell pins, but you'd be naive to think it doesn't happen.
"You can do it both ways, but if I really want a pin and I don't have anything they want, maybe I'll buy it," she said. But that's done away from prying eyes looking down from the roof above outside Stratford International station at the entrance to the Olympic Park.
They enjoy the camaraderie among people who have nothing in common, come from different corners around the world and meet up to swap stories and pins.
Linda Li, from Guangzhou, is in London for two weeks. Beijing, obviously, was big for her four years ago. But there's a thread when you talk to these collectors. It's something of a labour of love. They simply enjoy it.
It's not just crowds of spectators wearing them. Athletes have them attached to their accreditation "swingers" around their necks.
Linda, however, differs from most of the other collectors, who are proud of their finest items. Hers are not on display - "I keep them in my pocket."
There is an official range of Olympic pin badges for sale, and this year's batch include the various sporting disciplines, British landmarks, the London 2012 logo and the official mascots.