The Women's Motorcycle Contingent marks its 50th year leading the SF Pride Parade on Sunday. Their 1976 origin — a small group of women moving uninvited from the back of the march to the very front — changed how Pride parades open everywhere.

Before you see Dykes on Bikes, you hear them — hundreds of motorcycle engines turning over at once, building into a wall of sound before the first rider comes into view. That's been the opening act of the SF Pride Parade for exactly 50 years. Sunday's march is the anniversary.

The origin was unplanned. At the 1976 Gay Freedom Day March, a small group of women on motorcycles had been placed near the back of the parade. They moved themselves to the front. "We didn't want to be behind the gay men. We really wanted to claim our own space," Kate Brown, current president of the Women's Motorcycle Contingent — the organization's formal name — told ABC7 News. "We've always been pushing that boundary and being loud and saying, 'Here we are. See us.'"

They never moved back. San Francisco's chapter became the mother chapter, holding the trademark and licensing it to affiliates worldwide. Many of those chapters now open their own local Pride parades the same way, following SF's lead.

The legal backstory is worth knowing: the U.S. Patent and Trademark Office refused twice to let the group trademark their name, ruling the word "dyke" was disparaging. Dykes on Bikes challenged both rejections and won at the Supreme Court level — twice. "It was a major victory for LGBTQ rights, for freedom of expression — being able to take words of hate and say, 'This is exactly who we are,'" Brown said.

This year's contingent includes a detail that makes the anniversary specific: a flatbed truck following the riders will carry Brooke Oliver, the attorney who argued and won those Supreme Court fights, alongside one of the women who made the original move to the front in 1976.

The logistics: SF Pride Parade rolls Sunday, June 28, down Market Street. Dykes on Bikes leads — stake a spot near Beale and Market by 10 a.m. to catch them at the front. BART serves Embarcadero, Montgomery, and Powell; all three will be packed, so build in time. Full schedule at sfpride.org.

The tip: The engine roar is the signal. If you lose your spot in the crowd, you'll hear exactly where they are.