Yes. It is the rest for the end of a blade type stabilizer. If you dont have the Alko hitchead with friction pads, i suggest you either buy a blade stabilizer or change the hitch head to the newer design. Either solution but my pref would be the very simple job of changing the hitch head.
If you choose the latter you must check for an Alko compat towball.
Bulldog still make a blade type but it is extra weight.
Adding to Thingy’s post, if you go for the blade type you will need to fit the receiver behind the tow ball on your car. If you go for an Alko hitch you might need to change the ball on the car to accommodate it, the ball needs to be further from the car. If in doubt speak to an expert.