When a chassis moves onto the paint‑line transfer table, the operator flips the selector switch and the attached flag snaps into view, instantly indicating that the hydraulic lock is engaged and the line may start. In motor‑vehicle manufacturing this simple visual cue is mounted on control panels of welding robots, paint‑spray booths and final‑assembly stations. The flag’s position tells operators, safety‑interlock systems and nearby technicians which mode the equipment is in – for example “manual”, “automatic” or “maintenance”. Because the flag is visible from a distance, it eliminates the need to read small switch labels while the line is running at high speed, reducing the risk of starting a machine in the wrong configuration. It also serves as a quick check for quality‑control staff before a shift change, confirming that the previous cycle was correctly terminated. The same principle is applied in plant engineering, where the flag marks the status of large‑scale pumps or valve arrays. The flag therefore becomes the visual confirmation that a welding cell is ready for the next car body.