Merriam-Webster's Word of the Day for March 26, 2013 is:
hallmark \HAWL-mahrk\ noun
1 : a mark put on an article to indicate origin, purity, or genuineness 2 : a distinguishing characteristic, trait, or feature
The entertainer's new book features the same kind of wry humor that is the hallmark of his radio show.
"His usually sympathetic, sometimes overgenerous interpretation of others' motives has been a hallmark of his character at least since his student days." From an article by Hendrik Hertzberg in The New Yorker, February 4, 2013
Did you know?
Centuries ago, King Edward I of England decreed that gold and silver had to be tested and approved by master craftsmen before being sold. Later, London artisans were required to bring finished metal goods to Goldsmith's Hall to be checked, and if those items met the quality standards of the craft-masters there, they would be marked with a special stamp of approval. (The process is much the same today.) At first, people used "hallmark" to name that mark of excellence from Goldsmith's Hall, but over the years the word came to refer to any mark guaranteeing purity or genuineness, and eventually to name any sign of outstanding talent, creativity, or excellence.