Abstract: An assembly for generating an optical marking of the flight path of an air/space vehicle propelled by a power unit is associated with the power unit, and mixes the marking output of the generator with either the exhaust of the power unit or air streaming past the vehicle. The generator may generate smoke or steam. In the case of a smoke generator, the assembly may include an annular chamber surrounding a central passageway through which the power unit exhaust passes. The exhaust ignites a smoke-generating charge in the annular chamber, the smoke generated passing through bores in the annular chamber.