Summer might not be officially here yet, but signs already abound on the Metro transit system as the Washington region wilts under an early heat wave.

Hot stations and rail cars are already leaving some riders drenched in sweat. Tourists with cameras around their necks crowd around fare machines trying to figure out which pass to buy. And open-toed sandals and flip-flops are making their appearance, sometimes getting caught in Metro’s balky escalators.

Every summer, Metro officials say they see an uptick of incidents where riders get their shoes caught in one of the transit system’s 588 escalators. Rarely are there serious injuries other than maybe a stubbed toe or scrape.

But flip-flops are a special enemy of the moving staircases. Thinner soles make the summer footwear especially susceptible to getting caught, said Ken Sundberg, Metro’s assistant chief safety officer.

“The lip of your flip-flop may get stuck if you don’t carefully take the time to pick your feet up when you get to the top or bottom of an escalator,” he said. The shoes can get caught in a “comb,” a mechanism at the bottom that’s meant to trap debris, he said.

Metro keeps a box of flip-flops, sneakers and sandals pulled from escalators as reminders of what can happen.

“We have this concern every summer and urge caution,” Sundberg said of riding escalators.

The warmer weather doesn’t always mean flip-flops, either. Some locals adopt their own ways to show off their pedicures with cute open-toed shoes while commuting on the subway. The No. 1 tip: Watch your step.

Hazel Munroe of Hagerstown, who works as a legal assistant at a downtown firm, sports at least a three-inch pair of heels every day on her commute by bus and rail. The trick, she said while wearing a pair of black patent leather heels, is to pay careful attention when getting on an escalator at the start so you “catch the first step.”

“Then you set a pace and rhythm where you can just walk right up,” she said. Even when escalators aren’t broken, Munroe said she walks up in her heels. “The higher they are, the faster I go,” she said.

Footwear wasn’t a problem for a handful of art students from Denmark on their first tour of Washington recently. They mostly wore flats or sneakers, but navigating the Farecard machines and figuring out which train to get on proved a challenge.

“At the beginning it was a bit complicated, but now we’re getting it,” said Maria Slaeggerup, 19, who was on the next-to-last day of a week-long trip to the District.

Their problem: The Farecard machines are “so big and have lots of buttons,” said Signe Madsen, 21. And finding the train’s destination on the rail car seemed daunting until a teacher who had previously lived in Washington explained.

“Without him showing us how to use it, I’d have been lost,” said Kiki Stybe, 22.

Colette and Eric Mathewson of Visalia, Calif., got a real feel of Washington’s subway system one recent, warm afternoon when they had to carry their heavy suitcases down a broken escalator at the Gallery Place Metro stop as they tried to travel from their hotel in the District to another hotel in Northern Virginia.

“It’s not bad,” said Colette Mathewson, “until you had to do it with luggage.”

Although some locals get annoyed at the crowds of tourists and visitors to Washington in the summer, others take it in with a smile.

At the Smithsonian Metro stop during rush hour one afternoon, Sami Mousa, an IT contractor, waited for his Blue Line train to Franconia-Springfield on a crowded platform as school girls whistled and waved to passersby on the other side of the train tracks.

Mousa waved the girls and their chaperones onto a train.

“Let them go; they’ve been waiting,” he said. “Everything they see is new, exciting. It makes you happy to watch.”