This may seem like an obscure question but curiousity is getting the better of me!
On level 1-2 of Shinobi, there is a wall with six posters of Marylin Monroe. On five of the posters her famous beauty spot appears correctly beside her nose / lip, but on the sixth for some reason it's placed on her forehead between her eyebrows!
As odd as it may seem to be asking about a single pixel on a background, these backgrounds are usually generated as tiles copied over and over, which means the placement must deliberate so it seems like it must be an "Easter Egg" of some kind. Have the creators spoken on what the purpose of this is? Or is it a reference to something?