An experimental motorway symbol proposed by the Motorway Signs: Final Report of Advisory Committee for Traffic Signs on Motorways (Anderson report) as an alternative to the Economic Commission for Europe's proposed motorway symbol design. Members of the Anderson report disliked the ECE's proposed sign, due to it's tall rectangular shape, "over-representational", readability from a distance and lacked "instant impact". Eventually this symbol was replaced with the current 'motorway' symbol, which the committee had reworked to some satisfaction.
Motorway Signs: Final Report of Advisory Committee for Traffic Signs on Motorways - 1962.
Ministry of Transport