The signals on the Great Western Main Line west of Paddington for eastbound trains. The large numbers above the signals identify the national rail lines (the leftmost track is the London Underground Hammersmith & City Line) and I believe are a legacy of the Ladbroke Grove rail crash.
These signals being so close to the line terminus at Paddington can display only "danger" (red) or "caution" (yellow) aspects. Caution aspects are always accompanied by a route indicator of the platform number at Paddington into which the train will arrive.

This photograph was taken from the platform of the adjacent Royal Oak London Underground station.

Photo by Chris McKenna 31/05/2006.
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