It could be gone by the time you pick up those coins. On a city bus, let's say it's crowded. Keep your wallet or purse secure, in sight if it's in a purse, in your front pocket if a wallet. The biggest pick-pocketing activity goes on when there's a big boxing event or concert or sports event of any kind in town. Touirists are the biggest targets.
Pickpockets often work in pairs.
Don't get too adventureous after hours. The Strip and Downtown areas are safe from the most part but when a visitor moves to poorly-lit areas, away from the mainstream of action, unfamiliar with the area during the wee hours, there are desperate people out there. It's true in any city, but in Las Vegas, a visitor usually has cash and a visitor with cash can be a target of a professional thief. Keep valuables out of sight if driving your own car or even rent one. Computers, cameras, mini-cams, luggage, gifts with a fancy wrapping.