Holographs
Holographs (also - Holographis lasers or sky-writers) are used to project pictures or words onto a cloud cover, so that it can be seen by all troops of a battlefield. Holographs can be used to undermine enemy morale, reminding them about past defeats, promising comfort for deserters, and so on.[1]
Source
- 1: Warhammer 40,000: Rogue Trader. pg. 98
