The 47-year-old woman was hit on the leg by the signage, which was blown down by the wind, and had to be taken to Accident and Emergency.
Shoppers were sheltering from the rain underneath the overhang of the building at shortly after noon when a gust of wind blew the panelling off the shop front.
Anthony Le Boutillier was one of those trying to shelter from the rain.
He said: ‘I was going down the street and there was a heavy shower so I turned back and it just missed me.
Luckily people were sheltering under the building, so it just missed.
It was heavy stuff and there was a big crash.’ The Fire Service attended the scene and took down the remaining signage.