Hi,
When they're spreading it, you can't miss the ming of diesel around the workers and machinery, and the stuff leaches out of a newly-laid road surface first time it rains; also, when our diesel-powered car had a small fuel leak, it put a pretty substantial hole fairly quickly in the drive underneath.

If you don't have a diesel car (and I presume you wouldn't admit on here to owning a diesel bike

), next-best thing is probably the a little of the petrol in your bike's tank - dip a small stiff brush, like an old toothbrush, in the tank and give each stain a few good scrubs.
Hth.
Regards,