The “Find My” app is great for locating your iPhone and other Apple devices. But what about your keys, your bag, and all the rest of your important non-Apple belongings? Apple now has an answer for that: AirTags, stainless steel buttons that you can attach to your stuff and then track through the “Find My” app. They retail for $29 each or $99 for four, and you can purchase them starting Friday, April 30.

And to keep you from mixing up your AirTags with your roommate’s, Apple will also engrave them for free with up to four characters, which can be letters, numbers, or a few of about 30 emojis—including faces, gestures, real creatures, fantastical creatures, the skull, and the anthropomorphic poop. (If you’re going with all emojis, you can only fit three.)

You could always just put your initials on them.Apple

But, as is the case with vanity license plates and baby names, there are certain combinations of characters that are off-limits for your AirTags. According to Mashable, you can’t use the poop emoji after a horse, dog, pig, or bull emoji. If you’re hell-bent on having your AirTags convey an illustrated message about dragon poop, chicken poop, robot poop, or alien poop, those two-emoji combos are fine. So is the word hell, by the way, but poop and poo are not.

Butt and fart get the green light, though boob is banned (as is 8008, suggesting that at least some Apple engineers have typed that into their calculators before). Most of the obvious curse words are also on the “no” list, but you are allowed to choose FVCK or FUX if for some reason the F-word in all its thinly veiled iterations is important to you.

If you’re curious about what other innuendos you can sneak past the virtual guards, click “Add engraving” on the product page and come up with some of your own.

[h/t Mashable]