I'd have guessed it's a trench periscope too- it's not like any gunsight I've ever seen. Unless it has an inverted 'V' aiming point, it's not for a weapon. It's a simple periscope- it has no provision for adjusting the sight or mounting mechanism as, for example, the Slf.Z.F.1a/1 sight has (also a periscope), and I wouldn't be surprised if that's what this is being mistaken for. I've never seen a gun shield so hight that it would require such a tall periscope. And it's not Africa-tan- that's simply RAL7028 Dunkelgelb... it drives me NUTS that everything this color is automatically Afrika Korps!
Here's a real gunsight- the Slf.Z.F.1a/1
And here's the sight picture: