Being a former stonemason I was pleased to come across this set of illustrations in Frutiger’s masterpiece Signs and Symbols, a book I recommend unreservedly to anyone with an interest in the alphabet/scripts/lettering. (My edition is the 1989 single volume, published by Studio Editions, ISBN 1-85170-401-9.)
These marks are from Strasbourg Cathedral and date from a period between 1200 and 1700, with the top row being the earliest. Frutiger (who designed Univers) observes ‘the origin and development of stonemasons’ signs are closely associated with the social circumstances of the Middle Ages’.
Once masons were being paid, rather than working for the greater glory of God, they needed to mark the stone they had dressed to ensure payment.
[Click on image to enlarge.]