From comment above:
Heathrow's runways were originally numbered 1 - ... 8 ...
Tracking Lindbergh's employers & airports, from his job as the initial pilot working CAM #2 (commercial air mail route #2) in April 1926, to
Spirit of Saint Louis project of 1927, to his work with "The Lindbergh Line" transiting STL during 1930's, you can watch the runway designators change. Since the largest manufacturer then was Curtiss-Wright, the big factory at STL was first owned by Curtiss-Wright (McD bought it after WWII).
Using old mishap reports of 1940, each with the
airport diagram: prior to WWII the hard-surfaced rwys were designated with single-digit designators (anti-clockwise), with each approach-end having a designator-# from runway One to Six (so there were an even-number of rwy's).
Then after WWII, the web shows that aerial
photo of KSTL, with the magnetic-number system (the pre-war rwys still visible as today's taxiways):
http://www.usgennet.org/usa/mo/count...mbert-full.jpg
Edit -- Dec'1944, Chicago Convention & ICAO; Ch4, Article 37 "Int'l Stds", "... shall adopt ... international standards ... Characteristics of airports and landing areas" later ICAO Annex 14--Aerodromes ...