On my 19th birthday, along with three of my best friends, I made what was—with few exceptions—the most uncharacteristic decision of my entire life: I got a tattoo of a sun on my butt.

This was not, as it probably sounds, a hasty decision made while under the influence. It was planned, as true to our shared identities as anxiety-ridden honor roll students as it could have been. We scoped out the parlor weeks in advance, making sure it was clean and reputable. We thoroughly searched pain diagrams on Google Images, trying to determine just how bad getting a tattoo on your butt would feel. (As it turns out, it's just about the most painless place you can get one. Luckily for us.)

The sun, of course, didn't really mean anything. My friends and I had been feeling nostalgic, not for high school, exactly, but for the way it had brought us together. And so, instead of going Euro-railing or buying a pair of traveling pants, we did what any sane group of girls-turned-young women would do in such a situation: shelled out $75 each for a small outline done in black ink in locations ranging from lower back to hip to right in the middle of the cheek.

Tattoos, as it turns out, are amazingly easy to forget about. It's only when you compliment your cashier's sleeves at Starbucks and he asks you if you have any, or someone brings it up when you're playing "Never Have I Ever" that you're forced to come clean.

"You have a tattoo?"

"Cool!"

"Since when?"

And then the kicker:

"Where is it? Can I see?"

"Lower back," it turns out, is not a good answer. Neither is "Oh, you know... on my hip, sort of." When your co-worker says, very sweetly, "Oh, so you have a tramp stamp?" or your friend's mom trails off into horrified silence, you realize you've made a terrible mistake. It's the Catch-22 of butt tattoos: you're damned if you do, but you're most certainly damned if you don't.

I talked with my friends over winter break about this. They are all dating people at the moment, and when I asked how they had brought up the tattoos, all of them laughed. All of them had stories. And of course this isn't confined to just us: a different friend of mine who has a tattoo on her inner thigh told me a story about a guy she'd gone out with who had asked if it was temporary. People frequently mistake it for a birthmark. I myself have had to suffer through 20 minutes of unmitigated horror as I told my extended family, person by person, that I couldn't show them my "back tattoo" because it was still healing. Oftentimes, it seems, these tattoos are more trouble than they're worth.

But when I talked with my friends, I realized just how important they have been for us. For the rest of our lives, in every intimate relationship we have, we will explain, over and over, what these tattoos mean, who we got them with, what those people have meant and do mean to us.

For as long as I live, I will know that there are three people who did the same crazy thing as me, who were willing to stand with me and hold my hand while I experienced 20 minutes of needle-induced not-quite agony, and that I did the same for them. And no, it's not like we Eat-Pray-Loved our way across Europe, but we did change our bodies in a real, concrete way, for and with each other.

When I get asked, in the future, why I did this, I might say any number of things. Friendship, for one. Self-empowerment. I wanted to see what people would say. I have been told, before and after the day I turned 19, that getting a tattoo where I did is a sign of low self-esteem, or promiscuity, or lack of sexual self-confidence. And, unsurprisingly, I couldn't disagree more. Because I don't see what's disempowering about being able to see the marks of your female friendship, whatever form it takes, written on your body.

This is something that I will have, always. This is something that they will have, always. And sure, it's a promise of friendship and a recognition of change and all of those things, but it's also a record of a time when I loved some people enough to do something totally stupid with them. When I texted my other friends and (some) of my family the news and got their responses:

"Seriously?"

"It's not temporary or anything?"

"Pictures!"

"I'd ask for pictures, but I'm sitting in a restaurant right now."

"I can't believe you did that."

And now, eight months later, I catch a glimpse of myself in the mirror, and I am reminded: I can't believe I did either. The evidence of closeness, the circle and smaller triangles that spell out moments that have been and moments that will be for years to come: they never fail to surprise me.