If coins are rusty, you can always brushed them with Colgate.
I doubt you will ever see a coin that has gone rusty. Tarnished is perhaps, the word you mean. If you Google "Rusty Coins", you will see it has an alltogether different meaning.
Why not? The police are not going to target people who stay within the law. It's only the dick heads who think the laws of the land shouldn't apply to them, that are going to be fined.
Carefull about what you say about the police, they'll come down on you like a ton of bricks.