So, I was stealing things from Windhelm for the thieves guild when I ended up over-encumbered. I dropped a (stolen) sword, and a nearby guard came up to me and told me people could get hurt if I left weapons lying around. I gave him a hard time about it and the conversation ended with him saying "Well then, I guess I'll just have to charge you with disturbing the Jarl's peace." As he walked away I was notified that "10 Crime Gold" was added. I looked in my inventory but there was no "crime gold" and I'm not sure how my..."normal" gold was affected, if at all. A quick Google search showed that one other person had the same experience but they did not get any answers. I didn't find anything on UESP either. Anybody know what this is?

I think you need to check your bounty. It probably is what it means.

More than likely it was a bounty. Although the way bounties work is that it said "XX gold bounty added in *name of hold here*".

From the way it sounds is that it is a bounty of sorts but it was given in a different manner. It was a littering tax if you think about it.

On the spot fine? I'd take a look at the bounty, as Megatrons suggested.

(Being in rl law enforcement, I would suggest that the 'Ways and Means Act' has been used - jerk around the cop, and he'll find something to pin on you).

Ah...seems like that's it. Why would it say "crime gold" instead of just saying bounty added to wherever, though? Seems odd.

Bounty.
You got yourself a ticket.

That's actually really cool. I don't normally play thieving types (or throw swords on the ground) so I wouldn't know, but a guard giving you a warning and then deciding to give you a small fine for your back talk is pretty neat.

Just luck that the guard did not notice the sword was stolen.
He could also drag you to the jarl to pay the fine and he would take all you stolen items.

Happened to me in Oblivion, did not notice I was mostly naked until I had left town, I was wearing an stolen guard uniform