Dubbed "The Silver Screen", the LED screen faces an estimated 4.3 million drivers who take the M4 out of London to Heathrow each month.
Ocean Outdoor promised to unveil further "landmark, high-spec" LED screens across key locations in the capital before Christmas.
Damian Cox, chief executive of Ocean Outdoor, said: "We are committed to evolving the outdoor market through high quality, unique locations like this digital tower that will allow brands to communicate with commuters through an impactful and dynamic platform."
Ocean has sites at the Imax at Waterloo, and Europe's largest digital media wall located near Liverpool Lime St station.
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