Motorway gantry sign
A gantry spanning the motorway with blue overhead signs indicating one lane exiting and two continuing ahead, and the following text.
Left lane destinations: St Albans A414; Welham Green.
Right-hand two lanes destinations: London (M25) A1(M).
Junction number: 3.
The A414 is the North Orbital Road, a sort of 1930s precursor to the M25. It won't take you all the way around London, but a right turn here will allow you to use it as a shortcut to the anticlockwise M25, avoiding the jams at South Mimms.