Help with mystery z key locking gizmo identification.

[toolsntat]

Hello folks, just joined up here to see if anyone can shed any light on one of the items I have recently added to my collection of "tools and old tat".

This is the item and it has a keyhole in the shape of a "Z" but alas no key.
The curved arm is made really well from one section of metal wrapped around the pivot point then getting thinner,ending inside the lock as part of the latch.
From the look of it, myself and others who have seen this, say possibly leg or arm restraint but trying to find a reference online has yet eluded me :?:

Any idea's ?
Andy