An electronic device may be provided with optical markers. A marker may be formed from a coating. The coating may be patterned to form a two-dimensional optical code or may be patterned to form an outline or other recognizable marker structure that helps provide information about an electronic device. A device with a sensor such as a depth sensor or other sensor may gather information on the electronic device and its markers. This information may include information on images captured with an image sensor while the electronic device is illuminated by one or more light beams from the depth sensor or other light sources. Markers may be configured to serve as mixed reality optical markers in a mixed reality system. Analysis of the mixed reality marker images or other sensor data may reveal information on device type, device location, device size, device orientation, and other information on a marked device.