What is the cause of the green spot in this photoraph (Arrowed)?

I'm using a Nikon 55-200MM F/4-5.6 AF-S VR DX Black Lens with a Nikon 52Mm Filter Nc Neutral Colour, using the lens hood that came with the lens.
I do not want to remove the filter, but this could be the cause. It appears in all sorts of pics, usually just off centre. It is not a reflection of a signal light.
Is there a way to stop it happening?
It happens on two cameras too.

The first question is does this green "spot" show up in all your images.

My guess is that it is actually part of the railroad's signalling system