Not much really. Looks cool though. I suppose it's more of a decoration than "tech." About the only practical application of it is a tool to terrify the uneducated. The quantities of tritium the average person can buy are beyond harmless. You could breathe a hundred vials of the stuff and be completely unaffected. If you drank nothing but tritium water for several weeks, you would have some issues. But tiny vials with micrograms of tritium vapor inside? Utterly harmless.

Or, I suppose for the criminally minded, you could find some evil uses for it. You could probably rob a bank with it. "Give me all the money or I break this vial of radioactive vapor!" That would probably get you a wikipedia page, if you're just dying for your 5 minutes of fame. You could go down in history as, "that mad scientist that robbed a bank using radioactive gas." Of course it would be a bluff.

Though if you're just going to bluff your way through bank robbery, you can just stick your hand in a hoodie pocket for the same effect.

I suppose you could use it for other similar criminal acts of varied nobility. You could probably use the same bluff to create a hostage situation to bring awareness to whatever political/religious cause is your cup of tea. Ultimately most people are very ignorant of nuclear science, and simply the words "radioactive tritium" would cause people to shit themselves. And that fear could be harnessed for all sorts of malevolent purposes. (Even better as you can actually show people the faint glow from it, and prove that you do have something radioactive.)

Hmm... what else could you use tritium for? I suppose you could use it for religious purposes. Absolute quantities really don't matter much for that.

What else? You could tie it to a keychain and be able to find your keys in a dark room.

But really, it's mostly a novelty. I think small amounts of it can be used for gun sights. But in any quantity the average person could afford or legally be allowed to purchase, it's a harmless novelty. Larger quantities can be used in fusion reactor experiments and nuclear weapons. But if you try to acquire that much, you better have a budget in the millions, and the NRC is going to be on your ass. The average person can get a small vial of it that faintly glows blue in a dark room. It looks cool embedded in jewelry, but it really doesn't have much practical purposes beyond perhaps terrifying the ignorant. But I really don't consider malevolent uses to be truly practical applications.

(In case it isn't obvious, I do not endorse using radioactive tritium in the commission of any crime or act of violence or threat of violence.)