Well.... not sure if this actually was someone's escape route---no explanatory clipping on the back of this archival photo from the Baltimore Sun. All it says is 'Penitentiary--Maryland, 1956'; a quick skim in Google doesn't turn up anything obvious.
But what appeals to me most in this picture is the big black inset circle, which lends a graphic and abstract quality to the thing, especially with the dotted white lines and 'X.' I've got a small mini-collection of photos with such circles. They were intended, one surmises, to hold a cameo picture of somebody involved in the story.
Maybe I will post some of these 'black spots' tomorrow or the next day.