You know those super secure double-glazed front doors, with the kind of hook things that engage when you push the handle up?
You can spudger one of the glass units out and back in from the outside, without leaving a mark.
They look better than they are.
Most uPVC windows and doors should have the beads on the inside and a solid profile on the outside.
I have heard of someone cutting through all the plastic and pulling the glass out that way, though.
Both rather more obvious that surreptitiously jiggling the obscenely crappy Eurocylinder that the door came with.