You can buy turn signal kits which should go on pretty much any moped - they come with a switch/battery/wires and plug into your 'ped's electrical system to recharge. (they trickle charge the battery in the system) I've seen them crop up on ebay every once in a while, and several moped dealers should carry something like it. (I bought one years ago for my first moped, a bombardier puch maxi, I definitely recommend it as I suspect most drivers out there think hand signals are just you waving in a friendly manner!)