I guess if you don't know that a straight arm means left and a bent elbow means right - which, let's face it, a lot of people probably don't - then Zackees LED Turn Signal Gloves would be of great benefit, both to the cyclists wearing them and to the drivers looking at them. And even if you are savvy to the rules of signaling, nighttime riding or heavy traffic conditions can interfere with others' taking notice of an outstretched arm and its cyclist moving into their lane. In addition to clear signal markings, Zackees are also fitted with superbright LEDs that output 50 lumens of light per glove, and provide a wide-angle, 120-degree view to those around them. A built-in computer with ambient light sensors can even adjust the LEDs' power for daytime (4x boost) and night riding.
The gloves themselves are made of 80% spandex and 20% leather. Their electronics are fully washable and sweat/rainproof and, unlike mounted turn signals, travel to and from your bike with you, and so are far less likely to get stolen. Zackees signaling is controlled by a metal contact rivet between each glove's index finger and thumb. They can be activated with lifted arms, as well as with both hands on the handlebars for signaling to oncoming traffic.