I put turn signals on my bike and they work great. Look online for led motorcycle turn signals and order a set of four. These are large enough and bright enough to be seen in daylight. These also come with a threaded bolt that can be easily mounted though a hole that you can drill in a simple plate that you attach to your racks. If not you may have to fabricate a bracket as each bicycle is different. You need to have them far enough apart which is a little over a foot. Look at motorcycles and copy their spacing. If you put a large rear led light in the middle this will let drivers know what side is blinking and they can see the leds during the day and that is about all they see at night. Great for left turns. You can't use a normal auto turn signal flasher with leds so you need to get a model designed for the low current draw of leds. Now that motorcycles use a lot of leds more aftermarket flashers are available.

I use switches designed for electric scooters. These usually are designed for thinner diameter handlebars than motorcycles and have a bulit in turn signal switch, headlight switch - which you can wire to your front lights, and some times one or two extra buttons that you can customize.

I think cyclists should look to solutions reversed engineered from motorcycles and electric scooters since they have solved this problem years ago. Now that there are affordable lightweight, strong batteries available I think signals are a great edition to a commuter.

I am getting a new commuter this fall and will be putting my signals on it. I will be rebuilding the harness and mounting points and when I do I will post pictures.

Unless someones has tried truly daylight visible turn/brake signals they cannot say if they work or not. Trust me, when I tap my brake lever and my led truck light fires off then cars notice the same is true for the turn signals. Some drivers will not see you even if you have an armed escort though so be careful.