Final answer:
Trademarks during the Middle Ages became marks of quality and standards due to the regulatory role of guilds, assuring customers of the reliability and professionalism associated with the goods or services.
Step-by-step explanation:
Besides indicating the source of a good or service, trademarks changed with the emergence of guilds in the Middle Ages by becoming marks of quality and standards. Guilds were organizations of artisans and merchants who oversaw the practice of their craft/trade in a particular area. These guilds often enforced high professional standards and regulated the quality of goods and services produced by their members. Trademarks thus served not only as a means of identifying the source but also assured customers of a certain level of quality associated with the guild's reputation.