Although we've seen a few instances of Google's Project Glass in action, for the most part we have no idea how the glasses-based heads-up display will be controlled. One of the Google patents granted a few days ago, though, may give us some hints. The patent describes a wearable computing device whose interface can be controlled by infrared markers in the form of bracelets, rings, artificial fingernails, or effectively invisible temporary decals. A camera in the glasses would pick up radiation reflected from the marker, giving it a point of reference for user control.
The patent was filed last September and granted on May 15th, an incredibly quick turnover; it was granted for a "wearable marker" that could take the form of a "ring, bracelet, an artificial fingernail configuration... a decal configured to be affixed to a fingernail, or a glove, among other possible wearable items." This is no guarantee that Google will run with the system, but until you lost the ring or chipped the nail, it wouldn't be a bad idea. Besides, who doesn't want to use technology from Children of Men?