Signal before you start the turn, than hands back on the bars. Like groovestew said, "there could be a dozen reasons why you spilled - loose grit on the road, an irregularity in the pavement, could have just been a fluke."

I do better than half my riding at night, so I invested in Winkku turn signals. I feel much safer at night crossing four lanes of traffic with them. In daylight I use standard hand/arm signals, because, I am not sure of the visibility of the Winkku's in the daylight.