As Sihanoukville flourishes, so does petty crime. It is rarely serious, and mostly opportunistic, and certainly not something that should put you off visiting, but it’s a good idea to make the most of hotel safety-deposit boxes and keep an eye on your belongings when on the beach. Bag snatching, even from motos and tuk-tuks, is on the rise. As a rule, don’t carry anything with you that you can’t afford to lose.
Personal safety is another issue altogether; there have been several incidents of assault at Weather Station Hill/Victory Hill and along the dark unlit road to Otres Beach late at night, and drunken brawls are not uncommon, so it is safer to travel home by tuk-tuk rather than on foot or by moto, even around the main beaches.
Although none of this is anything to be paranoid about, it’s as well to ask your guesthouse when you arrive if there have been any recent incidents. Ultimately, the fun happens in the well-lit parts of town, so it shouldn’t be too hard to stick to them.