My car registration was stolen, should I be worried?

You asked, My car registration was stolen, should I be worried?

It's hard to give an exhaustive list, but in the end, I don't think that's really the important question to ask - really, the important question is, what should you do now to protect yourself? Reach out to the DMV and your insurer. Your state's DMV will have a process on how to replace stolen registration documents. The risk of not reporting them as stolen is that the thief may try to impersonate you with respect to your motor vehicle ownership (i.e. they may try to create an online account with the state DMV, or take over your existing account. Or they may try to get replacement plates and impersonate your vehicle, etc). Ask the major credit bureaus to lock your credit report. This will mean a minor hassle for you if you try to apply for credit any time soon, but it can help protect you from identity theft. The thieves now have your name and address and details about a vehicle you own - while that by itself isn't very powerful information, it may form a piece in a larger puzzle - taking steps to protect your identity can help prevent that.