Both Civil and Military airfields had ID circles, they were constructed after the first world war but removed shortly before the second. The circles were 100 - 150' across with letters 20' high, either within or near the circle. Many military airfields had bombing targets for practice and arrows to aid bombing runs. These figures were flush with the ground and made out of a variety of materials. Airport boundaries were also marked using straight lines.
National Grid Ref SK290310
Burnaston Aerodrome, Derby had a landing circle. Now under the Toyota factory.
National Grid Ref SW370297
St Just Aerodrome, Cornwall had a landing circle. The Aerodrome is still there the figures have gone.
These arrow figures still exist
National Grid Ref SP178839
Elmdon, Airport, Birmingham had a landing circle and an unidentified marker, the airport is now under Birmingham International airport.