Bicycle lights- Indicating in the dark
It's not clear from your question whether you ride regularly a bike, but really the best way to understand the requirements for a product like this is to get on a bike and do a bunch of riding around at night.

When you do this you'll find that the visibility of signalling at night is not as big a problem as all that. First, the proper approach to making a manoeuvre is look–signal–look–move: that is, you always check that it's safe to move and never presume that anyone has seen your signal. Second, bicycle position within the carriageway is a clear signal to other road users of your intentions: if you are positioned towards the left side of the carriageway, you intend to go straight on or left, and if you are positioned towards the right side of the carriageway then you intend to turn right. (Assuming drive-on-the-left as in the UK.)

Nonetheless, there might well be people who would like to buy lights to improve the visibility of their signals, so I'll make a couple more comments:


A device that clips on to clothing depends on you wearing long sleeves and so will not be usable in the summer.
If you're going to wear a light on your wrist for signalling then the light ought to be visible from all directions (so that it does not matter which way you put it on or how you hold your arm while signalling). The best shape would be a bracelet with lights all around.


So if I needed a device like this, I'd buy a SlapLit LED bracelet.