Abstract: A vehicle (e.g. aircraft) head-up display system having the capability of displaying, superimposed on an observer's view of the scene outside the vehicle, symbols representing information required by an observer in the vehicle, together with a pictorial representation of the vehicle environment produced by a signal source incorporating an imaging sensor. The signal source produces an output signal of raster scan format (e.g. a television type line-by-line scan format) and output signals of the same format representing the required symbols are developed by a storage/read out arrangement which stores the symbols in response to stroke writing mode signals and reads out the stored symbols in the same raster scan format as is employed by the signal source, the raster scan outputs of the storage/read out arrangement and the signal source being combined for application to the display unit of the system.