I think it's a sheet of paper caught in the wind. If you enlarge the image you can make out a shadow below it on the road, see attached.
Interesting snippet
here about that shop in the background called "The Tin Hat"
"When my grandfather, Arthur Cecil Scott, returned from the First World War, he set up a business at a shop at 21a Breck Road. He was by trade a master boot and shoemaker. He nailed his military 'tin hat' outside his shop in 1919. He and his family lived at 19 Letterstone Street, Everton. He died of paralysis due to gas poisoning as a result of the Great War, and is buried in Anfield Cemetery.
"In the late 60s, a cousin of mine, when coming home from school, went to retrieve the tin hat but the building had been demolished and the hat had disappeared."
Your letter struck a real chord with me, Ken. I remember the property in Breck Road which in later years became the 'Tin Hat' Sweet Shop well. This was run in the 50s by the family of one of my mother's great friends. I remember the 'Tin Hat' nailed above the door which had clearly survived for all of those years. If you enlarge the picture you can make out the actual tin hat on the pillar between the two doors, red line pointing to it on attached.
All swept aside back in the late 60's and now looks like
this around there. (Streetview)