ST. PETERSBURG — The first butts, perhaps, appeared in April on some steps behind the Sundial shopping plaza.

They were black marker scrawled on dirty, caution-yellow paint, about six inches tall, and shapely.

Three buttocks, formed by four unbroken lines. A simple yet mind-bending design that conjures a police lineup of backsides, or an alien race anatomically different from our own. They stood out among downtown's indecipherable graffiti, the signatures of bandit artists who mark up buildings undetected. People prone to walking might know of "blob dylan," and "dgen" and the person stenciling "fat guys with beards are everywhere."

But butts? On social media, a photo of the butts was a hit. They were kind of cute, people said, and definitely funny.

And then, the butts were everywhere. Dozens have appeared around the city since spring.

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A walk along Third Street between Fourth Avenue S and Central Avenue revealed what appeared to be an overnight butt spree, half a dozen more on the backs of signs and an empty display board outside a vacant nightclub. Soon they were on a pay phone in Williams Park, a trash bin in Old Northeast, the wall of an empty building in Grand Central and a utility box near the Morean Arts Center.

There were variations. Some had four cheeks. One on the restroom wall inside Black Crow Coffee has seven. Just this week, butts appeared on boards covering broken windows at the old YMCA building and along Second Avenue S.

Tagging seems to be on the rise, St. Petersburg Police officials say. The city's graffiti abatement program, which cleans up the tags, reports a 50 percent increase in calls to its graffiti hotline compared to this time last year. A weeklong project recently scrubbed 550 tags from the downtown corridor.

St. Petersburg assistant police chief James Previtera estimates maybe two or three people get arrested for tagging each year. The charge is misdemeanor criminal mischief, though if you've been convicted before, it can be a felony.

Generally, the few who get in trouble are caught in the act, or were tagging something someone really cared about.

"We're mostly concerned with investigating the graffiti that people report to us, the ones that cause real damage to private property that costs people money," Previtera said.

The city photographs and logs the address of every single tag it cleans up, so when a tagger gets caught, they can also be charged for previous work. Mostly, though, the taggers remain a mystery since the work is completed in seconds, in the dark, and with paint pens small enough to be concealed in a pocket.

As for the butts, the city's lone detective tasked with investigating graffiti is "very aware" of them, said St. Petersburg public information officer Yolanda Fernandez. Regina Williams, who runs the graffiti abatement program said, "Oh yeah, we've seen those." She chuckled about the butts, but made it crystal clear: "Graffiti is vandalism, and it takes a lot of work to clean up."

There's a sharp distinction between the type of street art St. Petersburg has become known for through its many murals, and graffiti, which is done without permission.

Muralist Johnny Vitale of the Vitale Bros. thinks a few taggers have some artistic skill, but are perhaps too lazy to do a mural, even though they live in a city where people are readily offering up blank walls. He has seen the butts, and admits they are pretty funny.

"It's an adrenaline rush to go out there and do that," Vitale said. "These kids — they're not even kids, they're adults — I think they do it for the rush."

Was that the motive behind the mysterious butt bandit? Adrenaline? For months, the tags offered no clues as to who might have the answer, or what the motives might be. Was it even one person? There could be a whole collective of butt-drawing taggers.

And then, a possible clue. A fresh butt appeared, mostly all alone, except for another conspicuous tag next to it: "neverfart."

Searching "#neverfart" on Instagram turned up, among many other accounts, an account for Soft Hoagie Rolls, which mostly posts photos of local skaters and zine-style collages. They'd also posted a somewhat familiar-looking butt drawing.

That butt photo led to the Instagram account of Jeremy Trevino, filled with pages on pages of butts in hilariously rendered situations. There are skateboarding butts, butts boxing each other, butts baking cookies. Those drawings look similar to the butt graffiti, but his are more detailed.

Trevino has even previously sold stickers featuring his own butt-centric art in St. Petersburg.

Did he do it? Has he tagged the butt onto the city?

"I can neither confirm nor deny that," Trevino said when reached by phone.

He did recognize the tags as using the design from his original drawings, which, he said, has been used by other people, "poorly." He even heard about someone getting a terrible tattoo of it.

Why does he think the person who is tagging the butt graffiti is doing it?

"For the laughs," he said. "Part of it is probably just knowing these mature, grown, white-collar people are looking at these lowbrow butts."