Starting about two weeks ago, motorcycle owners say seats of bikes left on the street at night have been slashed, many of them with an odd, square cutout.

"It seems like some somebody is doing it to have some sort of souvenir," said Joshua Stenseth, who woke up Wednesday to find a patch removed from the seat of his 2003 Suzuki SV650. He walked down Northeast Hancock Street and found the same had been done to two other motorcycles.

Ginger McCabe, who runs motorcycle upholsterer New Church Moto, says she's heard of "literally hundreds" of incidents like this. She posted to her business's Facebook page on Sep. 2, "Portland motorcyclists: there is someone in town who is slashing seats ... Any help or leads or eyes kept out would be much appreciated. Lets catch this fucker!"

The Portland Police Bureau has been dealing with a rash of car vandalisms since May — 300 since then according to figures released last week (they even have a map). But the upswing in motorcycle vandalisms is new.

A square patch is commonly removed with the slashings, but not always. Sometimes the seats are simply jabbed with what could be a box cutter. And sometimes the tires are slashed, but not in a way that the rider would notice. The tired are punctured with what could be a large needle, leaving a tiny hole. It's been happening to cars so often since May that people call it getting "pinned."

But with motorcycles, the clandestine tire pinning is more dangerous. Motorcycle owner Marc Friedman says unlike in a car, when a bump signals that your tire is flat, on a motorcycle "the first time you notice is when you're sliding down the road."

Motorcycle owners have been posting about the incidents on Instagram, and one of them, Tony Morgan, made a map of his own. It's not complete, of course, but it shows the motorcycle slashings seem to be located around the Alberta and Buckman areas.

"Whoever is doing it probably lives in those areas," Morgan speculates. "Those kind of random things seem to be in places that are familiar to people."

That said, Morgan points to posts bragging about vehicle vandalism on anarchist websites as clues to who the vandal might be. "I don't think it's a random act like tagging a wall or something," Morgan says. "It seems very specific, like someone is trying to prove a point or has some weird logic to it."

Friedman, who works at biker hangout See See Motor Cafe, disagrees. "If it was $25,000 Ducatis that were getting slashed all over the place, I could see a misguided anarchist kid doing it," he says, "but these are by and large 20- to 25-year-old Japanese bikes. I'd say the average value of things getting slashed is under 10 grand."

"It doesn't seem to have any sense behind it," Friedman says.