Which architectural element became so synonymous with a specific architect's brand identity that it was trademarked as part of their visual signature?

In the world of architecture, brand identity plays a crucial role in how firms are perceived and remembered. Major architectural firms often develop distinct design languages that become instantly recognizable in their buildings. This trivia question tests your knowledge of how certain architectural elements have become synonymous with specific architects and their brand positioning in the industry.

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Frank Gehry's undulating titanium façades
I.M. Pei's glass pyramid structures
Michael Graves' blue scaffolding during construction projects
Richard Meier's white enamel panels with specific proportional systems