My grandmother spraypainted trains. On the street she was known as Batman, because so few people knew who she was or what she did. Kind of like Banksy, maybe.

What she did was not tagging, not according to her (I would learn later from her peers). Tagging is gross and uncivilized, she said. She was an artist, and so are the other train painters. They don’t do it for money or public acclaim, they do it to both beautify and to rebel.

Grandma was seventy. To the rest of the world, she was a short, hunched, Little Old Church Lady. She spoke softly but laughed loudly. She shuffled more than walked and wore glasses thicker than windshields.

Like in one of those Christopher Nolan movies with Christian Bale where his sort-of girlfriend touches Bruce Wayne’s face and says that that’s the real mask, the “Grandma” that Grandma showed people was a front. A mask. Perfect, too, because who on earth would ever suspect that secretly, she maintained a two-minute strict plank, or that on some nights she sneaked out of her house and painted colorful murals on the sides of boxcars?

She stayed in better shape than me. I just watched a lot of Netflix. Not even Netflix and Chill. More like Netflix and Cheetos.

I’d seen some of her work, driving her to church each Sunday. I didn’t know it was her until just recently, when I happened to be staying over while my apartment complex was being fumigated. I was having trouble getting to sleep when I heard her sneaking out of the kitchen door.

I got up, thinking she must be sleepwalking, but peeking through the crack in the door, I saw she was wearing a backpack. Cans rattled inside. She slipped out, and I hurried to follow, and that’s when I found out. She walked three blocks, keeping to shadows like some kind of elderly ninja, until reaching the tracks. I stayed back and watched in awe as my old granny hit the side of a boxcar with quick flourishes and long strokes of her arm that left me stunned.

I managed to get back to the house without her knowing I’d seen. The next day was Sunday, and I watched her as we drove. She got the tiniest little smirk on her face as we went past her handiwork: a giant rainbow arching over several of our town landmarks. In the sunlight, the artwork gleamed.

Grandma kept her escapades down to maybe twice a month, to the best I could tell. I don’t know for how long it went on, but from the night I first caught her, she spent two years out there making her art. I was jealous, to be honest, and wanted to ask her about it: Why do it? When did you start? Shouldn’t you get paid?

I only got answers to those questions from other artists after she died.

Her identity as the artist known as “Batman” only came to light publicly when she was found early one Sunday morning, a can of red paint in her hand. In her bag were six other cans, plus a sandwich baggie full of various spray paint can tips. I hadn’t even known there was such a thing as different tips, but each, it turns out, sent the spray in a particular manner. I guess to understand, you had to be an artist.

Had the police thought to do it, they probably could have arrested dozens of graffiti artists at her funeral, because there were three distinct groups who crammed into her church for the service: our few remaining family, her Old Church Ladies . . . and then this rag-tag group of people, mostly men, who looked like they were either experiencing homelessness or had just come from a Jackson Pollock studio. They were quiet and respectful throughout, despite some of the church folks giving them and their paint-stained satchels a once-over glare.

After the church service, everyone went to the cemetery. I found it interesting that Grandma’s casket was unadorned. As an artist, I’d have thought she’d want something at least quirky, if not grand.

Everyone sat still, many of us quietly crying, as the minister spoke the last few words over Grandma’s casket. Then, before anyone could have stopped it, the minister gestured toward the artists and took a long step backward.

The first of the group approached the casket pulled a spray paint can from his satchel and set to work.

A few gasps went up from the crowd. I don’t blame them. But since there were at least as many artists as there were church folk, no one made a move to stop them. They were far too scary.

A second artist joined the first. Then a third. They took turns, of a sort, spray-painting Grandma’s casket in small groups. Sometimes one would paint over another, and none of them seemed to mind.

We all watched them work. The general sense I got from the mourners can only be described at first as “horror.” It then gradually cross-faded to “curiosity.” By the time the last artist stepped back and the group admired their own work, the sense in the crowd had turned to awe.

It seemed wrong to applaud, yet I wanted to. I watched as the artists traded hand slaps, hand shakes, back pats, and hugs, before flashing peace signs at the rest of us and wandering out of the cemetery together. I expected at least one to paint a headstone, but no one did.

Then they were gone. I never knew their names. And Grandma’s casket gleamed, like her own paintings, beneath the sun.