New legislation has it that you must have a valid permit to operate a motorbike in Sihnanoukville. Of course locals arent getting stopped but many of foreigners who have rented bikes have been. Usually they hold the bike and send you back to the rental company to retrieve your passport and the owner of the rental co. to retrieve the bike. A valid permit would be a Khmer license or an International Drivers license. If coming from the USA take the time to pick up an international license from AAA. Cost is 10 dollars valid for one year. I havent heard of any major problems from the guys living in Kampong Som but they are getting their Cambodian licenses. This hasnt spread thru the rest of the country but there is the possibility.