In what TOS episode did Spock first wear the IDIC symbol?

Answer 1

Mr. Spock first wore the IDIC symbol as a pendant around his neck in the Star Trek: The Original Series episode "Is There In Truth No Beauty?" Jean Lissette Aroeste wrote the installment.

Leonard Nimoy was rather reluctant to wear the pendant, since Gene Roddenberry had commissioned its design to be marketed through the marketing firm Lincoln Enterprises, now the store division of the net-site http://www.Roddenberry.com/, and essentially shoehorned it into the story. But over the years, it became something of a Vulcan planetary symbol. A Vulcan phrase, Kol-Ut-Shan, was even coined to mean the same thing.