California

https://www.msn.com/en-us/news/us/thieves-are-now-targeting-fire-hydrants-across-los-angeles-county/ar-BB1nD01E

It sounds like police need to crack down on scrap-yards. Stop the flow of money, then the wire and hydrants will stop disappearing.
I was talking about this solution with some friends, and one of them said that the thieves could melt down the hydrants and sell them, because the scrap-yards wouldn't know that they were stolen hydrants. I compared it to fishing, and how if the game wardens catch you with a cooler full of fish fillets in your boat, they are going to hit you with a charge of keeping an illegal fish for each pair of fillets. If you don't preserve the fish in a recognizable form, they will assume those fish were a protected species and fine you accordingly.