When I had my 50cc motorbike (limited to 30mph and fully legal without license or registration) I was stopped at a police checkpoint. When they found out I was a foreigner, the two cops spoke to each other for a while then one came back to me saying that I needed a plate and proper ID (I don't carry my passport in case I get robbed, I carry a photocopy). They said they would impound my bike and I'd have to pay roughly US$450 to get it back.
Or...
Perhaps I could pay a smaller 'fine' now and be on my way. "How much?", I said. "How much have you got?", he answered. I got my wallet out to check and he quickly told me to put it away, looking around nervously. I was carrying almost nothing so I told him he'd have to impound my bike. He explained it to me again, as I had obviously had not understood correctly. He gestured toward a nearby petrol station with an ATM and suggested approx. US$90 would cover the fine. He also requested I fold the money up inside my paperwork out of sight. A friend warned me that cops here often plant drugs or fabricate evidence when you get on the wrong side of them. I was soon on my way again...
Since then I've avoided main routes where they set up checkpoints and have recently sold the motorbike. The other week I went through a checkpoint on my motorized bicycle and they didn't stop me so I'm feeling a bit less stressed when I ride now. I wasn't doing anything illegal, but it seems that the cops here aren't as law-abiding as me!