UV Pen Ultraviolet Invisible Ink Continuity Markers - Blue, Pink, Yellow

Television, Film and Theater Art Directors use UV Color Markers to mark prop positions, set piece placements or beverage levels while remaining invisible to the naked eye and camera. 

This ensures that props remain in place or that set pieces are consistently positioned, especially in long-form productions or scenes involving extensive editing. Camera Assistants may use the same technique to make starting toe marks for talent positions.