Whatchamacallit

I don't know what this is but I've seen a few of them in different back streets.  This is the most complete one I've seen; all the others have had large chunks missing but they've all been the same lovely rusty colour.  This one also has what I'm assuming is a makers mark in the middle section; I've put a close up of it in extras.  It looks like a gap in the wall underneath the rusty header has been filled in so I'm wondering if they had anything to do with coal deliveries to the houses?