Pop quiz - do you know your standard street hand signals? They're quite easy. Left arm up for right turn, left arm straight out for left turn, and down for a stop.
And important as they are (and essential! Please use them! It's the law.), I can't help but get super excited about the next stage of signaling technology - namely, actual lights!
This tutorial uses "conductive thread and sewable electronics so your jacket will be soft and wearable and washable when you're done. Enjoy!"