I have a Cobra and an Agent that I have shot quite a bit, but they don't have any rachet marks (yet). I got them both used and they were shot no doubt before I got them also. Sorry, I don't have any rachet peened agents or cobras. Just look at the area around the cylinder pin at the(inside) back of the frame-If its peened,it will be readily visible.
I think they would be shallow 'dents' and displaced material from where the Cylinder Ratchet back-sets against the Recoil shield when firing Ammunition which is a little too hot for the design of the Revolver, or, for an aluminum Alloy Revolver, maybe this ends up occurring over so-many-rounds, regardless.
Cylinder to Forcing Cone gap would likely end up enlarging with this.
I do not recall ever seeing any images though, other than rarely, and on Steel Frame Colts, glimpsed in passing on Gunbroker.