GEOFF BENNETT: Spray-painted words and pictures, usually clandestine and often illegal, are getting erased by a group of New Englanders who have tagged themselves the - - quote -- "anti-graffiti vigilantes."

But, as Pamela Watts of Rhode Island PBS Weekly reports, the method they employ against the perpetrators is an art in itself.

The story is part of our arts and culture series, Canvas.

HOLLEY FLAGG, Artist: I love those rocks, yes.

They're my friends.

I have known them forever.

So I take it very personally when people deface them and put terrible things on them.

PAMELA WATTS: Artist Holley Flagg has good reason to be protective of the breathtaking rocks that define the 400 miles of Rhode Island's rugged coastline.

It is the view right out the window of her third-floor studio in the home her family has lived in for generations.

The rocks were her childhood playground.

HOLLEY FLAGG: Grew up there, picnicked there, ran all over the rocks, know them like the back of my hand.

Also, I'm an artist, so I really love the beauty of them.

They're just unique rocks.

PAMELA WATTS: Raw natural beauty is the bedrock of Flagg's work.

She's currently painting watercolors of nebula from images captured by NASA's Hubble space telescope.

HOLLEY FLAGG: This is Madam Butterfly.

PAMELA WATTS: Flagg is also a graphic artist, creating designs for the Metropolitan Opera and the Museum of Natural History in New York.

But when so-called street art, spray-painted graffiti, began proliferating along the rocks in her Narragansett neighborhood, the artist saw red.

HOLLEY FLAGG: When you see somebody defacing them and writing their personal messages, which they think are going to be immortal, all over the rocks, it's really upsetting to me, and I just -- it's visceral.

PAMELA WATTS: Flagg was so outraged, she took justice into her own hands, forming the citizens group Anti-Graffiti Vigilantes.

HOLLEY FLAGG: Just lightly brush over it like this.

PAMELA WATTS: Armed with only a brush and cans of latex house paint, she started taking a swipe at what she views as crimes against nature.

HOLLEY FLAGG: Let's see what color you got.

That looks good.

PAMELA WATTS: Soon, a small posse of like-minded volunteers took up the charge.

Their restoration of these geologic gems requires wiping out the words and pictures in such a way it tricks the eye.

Instead of just a cover-up, the rocks magically appear as they once were.

HOLLEY FLAGG: I judge how close I am with the color that I have put on.

Really, the key to a good job is to just feather it in really lightly, let the texture of the rock come through.

PAMELA WATTS: At first, they tried to clean off the spray paint with wire brushes, even chemicals.

Nothing worked because the rocks were too porous.

The beach was too steep for sandblasting equipment, so: HOLLEY FLAGG: I know about painting and colors and nuance.

So we said, let's try painting over it, camouflage.

PAMELA WATTS: How did you come up with this technique of camouflage?

HOLLEY FLAGG: I didn't really think about it.

It was just very basic.

How do I make this look like the rock there?

I keep adjusting my paint colors as I go along.

You keep doing it until you like the effect that you have gotten.

PAMELA WATTS: Because the rocks are different.

Some are granite.

Some are brown.

So you have to pick the colors?

HOLLEY FLAGG: Yes.

And you do many colors over one little area of rock.

You don't just say, OK, this rock is gray.

Here's gray.

JOAN PAVLINSKY, Artist: Get a big dry brush and you just smash it into the rock.

I think it's more just feel than anything.

PAMELA WATTS: Joan Pavlinsky is a social worker, artist, and determined to restore the rocks to their natural state.

JOAN PAVLINSKY: It's just a way of kind of making my own mark by marking over other people's work.

If you think about what art really is, it's mark-making.

And, hopefully, we're creating an environment so that it's not going to be vandalized again.

MARIANNE CHRONLEY, Anti-Graffiti Vigilantes: If we do a good job, then they can't tell where it was.

So that's what we're hoping, that, as you walk around here, you don't even think about graffiti.

It's just not what you came here to see.

PAMELA WATTS: Volunteer Marianne Chronley joined the group a decade ago.

Spring and autumn, the band of avengers attack rocks at places like this.

Chronley says they gather tips from informants.

MARIANNE CHRONLEY: We watch for it and we hear about it.

People tell us about it.

When we hear that it's down here, we say, all right, we all -- we have got to get a crew together and come on down.

(LAUGHTER) PAMELA WATTS: The Anti-Graffiti Vigilantes say those who come to stroll along the shore often voice appreciation and sometimes offer to help.

HOLLEY FLAGG: A lot of people say, oh, I'm so glad you're doing that.

And then other people are totally blank and have no clue what we're doing.

And they just think this is a bunch of weird people.

PAMELA WATTS: Undaunted, they keep chipping away, true rock stars of Rhode Island's shores.

HOLLEY FLAGG: I want you to be able to look at these beautiful rocks and not read things, no words, no images, just say, wow, these rocks are really beautiful, this ocean is beautiful, and we're so grateful to have it.

PAMELA WATTS: For the "PBS NewsHour," I'm Pamela Watts in Narragansett, Florida.