What is this above my window?

[imanovicehelp]

Hi all,

Not sure how to describe it but it looks like there's a black/grey lining running across the bay window and looks in need of repair. It has nails/screws in it at sections? Not sure what you would call it. Can anyone help? Do I just need a coat of bitumen paint? Thanks!

 

[Tigercubrider]

Looks like flashing? There is probably a timber behind it, supporting the wall or the render.
It could be lead, aluminium or other