What does this phrase "They ain't got a thing on me" mean?? it's from an Iron Maiden song?

Question

What about the english grammar of the phrase, is it ok??

here is the lyric...

Just sixteen, a pickup truck, out of money, out of luck.
I've got nowhere to call my own, hit the gas, and here I go.

[Chorus]
I'm running free yeah, I'm running free.
I'm running free yeah, Oh I'm running free.

Spent the night in an L. A. jail, and listened to the sirens wail.
They ain't got a thing on me, I'm running wild, I'm running free.

[Chorus]

Puller here at the Bottle Top, whiskey, dancing, disco hop.
Now all the boys are after me, and that's the way it's gonna be

Answer 1

They have nothing on me. I am innocent in other words

Answer 2

I think that You will find that this expression goes back to at least the 1930,s when it was used in "Gangster" movies. It means, quite literally what it says, "They" (the police) can not prove Their allegations of a crime because there is either sufficient evidence, or "I" didn't commit the crime.

(Ah, the pleasures of a misspent youth wasted watching black and white movies. And to think 'they' all said it would never come in handy!)