The photo below shows a "C" shaped cutout in the frame rail of a 1/2 ton low rider pickup truck. The mouth of the "C" faces the rear axle, and was made to allow room for the axle to move up and down without striking the frame. The cutout significantly weakens the frame of the pickup and could result in the frame breaking while the vehicle was being driven.
This is an "out of service" condition. The vehicle was issued a Notice & Order removing it from the highway immediately and a tow truck was called.
To repair this condition, the vehicle owner must replace the frame, or have the frame repaired by a certified welder at a body shop. The truck cannot be driven or parked on a highway until the repair is completed and the vehicle inspection passed.
Making changes of any sort to a vehicle's frame must be done with caution. Check with an inspection facility before cutting, drilling or welding anything to a frame to insure that the modification will pass inspection and be safe.