Smart Motorway gantry sign
A gantry structure spanning the motorway with electronic signals, blue signs showing the left lane exiting and three others continuing ahead, and the following text.
Exit destinations: M1 ; The NORTH; Luton [Airport symbol].
Forward destinations: (M11), Hatfield (A1(M)); Stansted [Airport symbol] Dartford Crossing M25 .
Junction number: 21.
Change Route: M1 The NORTH
That catch-all phrase "The NORTH" is standing in for most of the UK at this point, embracing everywhere from Milton Keynes to Inverness. Exit here for flat caps, whippets, bagpipes... and Luton Airport.