What does a green light slowly waved side to side below waist height mean?

A green light slowly waved side to side below waist height signifies "Proceed at caution." This signal indicates that while there is a general approval to move forward, it is essential to do so with heightened awareness and attentiveness to surroundings or potential hazards. It serves as a critical reminder to observe and assess any conditions that may affect safe movement, such as other trains, maintenance activities, or potential obstacles on the track. Caution is necessary to ensure safety since it does not imply unrestricted clearance to proceed without consideration.