I’m standing this evening on the balcony of a prison guard tower, the wind whipping fiercely as purple rain clouds roll into Raleigh. Next to me, a high-school student shuttles a can of spray paint back and forth, laying on a thick, drippy coat of neon green.

About 30 young people crowd around us, busily adorning this tower and a second one with a labyrinth of graffiti. On every side, aerosol cans are hissing. A stack of “Easley for Governor” placards sits on the ground, waiting to be cut into stencils.

Until 1998, these guard towers on Blue Ridge Road marked the edge of the Polk Youth Institution, a state juvenile prison. The razor wire, guards and inmates are gone, but the old buildings remain. Recently, staff at the North Carolina Museum of Art next door have claimed the towers for art installations. This one, called “Physical Graffiti,” is inspired by Chinese artist Xu Bing, whose exhibit just opened at the museum.

In his works, Bing often creates his own pictorial language, mixing Chinese characters with symbols and English words. Mindful of his example, museum staff chose a group of Triangle high-school students and local artists to create their own graffiti language on the towers.

Since its emergence in the 1960s and ’70s, street art has won many supporters in the museum world. And graffiti is embraced worldwide as a forceful, public language for anyone with a message and a marker. Still, there’s a stigma attached. In many quarters, graffiti’s considered vandalism. That’s where “Physical Graffiti” takes a risk. A group of kids merrily “defacing” state-owned buildings might well raise the eyebrows of passers-by and public officials. But startling people is the point, museum officials say. So is drawing new visitors to the galleries.

On this evening, the towers certainly do draw attention. Passing motorists honk and cheer. On the balcony of the second tower, Ryan Thoma, a senior at Sanderson High School in Raleigh, is dabbing paint onto his “tag,” or personal logo.

“There’s not a lot of graffiti around this part of Raleigh,” he says. “But on the guard towers here it looks striking and rebellious.

“It’s like being at school and carving your name on the desk,” Thoma adds. “You’re leaving a little legacy.”

As he speaks, a rainstorm moves in and lightning creases the sky over the old prison. Reluctantly, staff members wave the artists toward shelter. Walking to my car, completely drenched, I wonder how people will interpret the tower installation. Will passing drivers see it as art work, or an irreverent eyesore? Graffiti is a litmus test. It forces you to choose sides: The property owners or the so-called vandals?

Or maybe graffiti, as Thoma says, is mainly a way of reclaiming public space. Whatever this prison meant before, it’s been rededicated.