The racks with 1 ¼" & 1 ¼" w/ 2" adapter do not have a provision for a safety pin. These racks are supplied with a velcro strap that attaches to the safety chain loops on the receiver. I've always used it since it takes all of 15 seconds to attach and is cheap insurance against the rack and my bike skidding down the road at 70 mph.

The racks with the 2" hitch come with a provision for a pin or lock that goes through the receiver and hitch bar.