The only affordance of such a plate is its push-ability, and the fact that someone actively installed a metal plate (instead of just relying on the door's natural flatness), as well as its location at the point of maximum leverage (all the way to the right of the door, in the door's vertical center), is a clear signifier for such push-ability.
Not only that, but it does its job without offering any other confusing affordances (such as a vertical handle which is also technically pushable, but which many would interpret as being meant to be pulled).
Whenever I need a relatable, succinct example of affordances and signifiers for my engineering comrades, I turn to this one. Anyone interested in design is doing themselves a dis-service by not reading Don Norman's classic.