When you get right up to the top floor of Salts Mill, you can see, through the glass skylights, a hazy glimpse of the weathervane that sits atop one of the twin towers on the roof. The glass is dirty and criss-crossed with strengthening bars, so it is pretty much impossible to get a decent photo of the weathervane from there, which is a pity. It is quite attractive, with a nice font and an ornate pointer. I have done some complicated manipulation of this image to achieve this effect! I quite like it. It's not 'the truth' but it's not far off what you can see beyond the dirt and the iron bars. (The N/S axis is all but invisible when it points straight towards you.)
For the purists, here's one taken from the outside, with my telephoto lens on max!