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The "30" and "25" are the speed limits in m/hr for the Metropolitan and Piccadilly Lines respectively. Below the "25" is the triangular rail gap indicator, which shows three red lights if current is off on the section ahead.
Just visible to the right of the signal is a "D" board showing "D off". This is to inform drivers that the train carried de-icing equipment should be switched off.
Almost obscuring the signal is the grey cabinet on the platform housing the CCTV monitors used by the drivers to check the platform before closing the doors.