From the end of the 13th century to the early 19th century, craftsmen across medieval Europe were organized into unions called guilds. These guilds were responsible for developing strict rules for product and service quality. Inspection committees enforced the rules by marking flawless goods with a special mark or symbol.

Craftsmen themselves often placed a second mark on the goods they produced. At first this mark was used to track the origin of faulty items. But over time the mark came to represent a craftsman’s good reputation. For example, stonemasons’ marks symbolized each guild member’s obligation to satisfy his customers and enhance the trade’s reputation.

Inspection marks and master-craftsmen marks served as proof of quality for customers throughout medieval Europe. This approach to manufacturing quality was dominant until the Industrial Revolution in the early 19th century.