The 85-year-old woman, who does not wish to be named, sustained a deep cut that required 13 stitches in the incident at Wardroper House on St Georges Rd, Southwark on 15 July 2010.
She was hospitalised for eight days before eventually making a full recovery.
Westminster Magistrates’ Court heard yesterday that Durkan Ltd was responsible for the hoarding which stood alongside a pavement outside the ongoing development.
An HSE investigation identified that it was poorly maintained, badly designed and constructed, and had been overloaded with advertising material.
Magistrates were told that had the hoarding been properly designed and maintained to withstand a specific weight and inclement weather, then the incident could have been avoided.
Durkan of Waltham Cross, Herts, was fined a total of £5,000 and ordered to pay £6,000 in costs after pleading guilty to a safety breach.
After the hearing HSE Inspector Toby Webb said: “Advertising hoardings of this nature are defined as temporary works and must be properly designed, constructed and maintained to ensure they are safe.
“This sign and hoarding was not maintained in a safe condition, and a pensioner was seriously injured as a result.
“She could have been killed, and there was a clear risk to other passers-by as well as workers on the construction site it served.
“Durkan Ltd could and should done more to prevent that risk.”