Looks a lot like a carburetor float needle to me. It allows the flow of gasoline into the float bowl, which sets the amount of fuel fed into the engine.
It’s common for float needles (and carb parts in general) to be made of brass, and the wire clip being made out of steel is also consistent with a float needle. The plastic tip is probably used for a better seal when the float is up, closing the needle port.
I’m assuming there was no ID or contact info with it, since you probably wouldn’t be asking if there was.
Hypothetically, if you were to give it to the police, how would the police know that who the rightful owner is? If I walk into a police station right now and say I lost $200, do you think they would hand over $200 to me? No, I have no way of proving thats my money, and they wouldn’t believe me for a second.
Keep it. Lord knows everyone could probably use an extra few hundred bucks these days…