Apple is always patenting things, and only a few ever are actually made, but here are a few interesting ones dug up by Apple Insider. They relate to putting information on a transparent display, more specifically a hybrid display that can overlay info on the transparent bit, but also has a layer that can be made opaque, on which to put normal text and images.
They envision a sort of sightseeing situation, where the device has GPS and wi-fi data informing it of its location and streaming data, while the camera and transparent screen work together to, say, label buildings or parts of a piece of art. It would also be possible to provide real-time updates and an AR overlay of the location of other people or waypoints. Handy.
As for the opaque/transparent thing, imagine an e-paper-like screen sandwiched in there that can be switched between clear and opaque. There are already OLED panels that do this – kind of.
Sounds solid to me. Now they just have to actually invent this make-believe stuff. Here’s the first patent (Synchronized, Interactive AR Displays for Multifunction Devices) and the second (Transparent Electronic Device).