The phrase "a defining mark" is correct and usable in written English.
It can be used to describe a characteristic or feature that clearly distinguishes someone or something.
Example: "The artist's unique style is a defining mark of her work, setting it apart from others in the genre."
Alternatives: "a distinguishing feature" or "a hallmark characteristic".
That is a defining mark of a True Teacher of Shinran's True Teaching.
When will parents again resume the easy confidence in parish priests that was once a defining mark of Catholic life?
Late last winter, the phenomenon achieved a defining mark of cultural validity when CBS Interactive set a reality show inside a gaming house.
What results is an expansive, variegated, and sometimes even contradictory vision in which the strange becomes not alien but a defining mark of everyday life.
It's a defining mark of modernity not to take actions at face value but to consider them in relation to origins and personal histories, and even to take their connection to individual backstories as emotionally and morally primary.
For the young women of the novel, though, the time is critical; the crisis they face will become the black dot on their time line, a defining mark pointing to the good or bad luck they are about to suffer.
The ultimate culmination of those things that my generation has been sorely left out of, is perhaps the other defining mark of an adult, at least where the "American Dream" is concerned: the ability to own a home.
Lee's surrender at Appomattox in April 1865 ended the partnership without a defining punctuation mark.
Her desire to absorb as much experience as possible in life outstrips even her ambition – which is large – to make a defining scientific mark.
An Iranian dessert made of thin vermicelli noodles that are suspended in a sugar-and-rose-water syrup, faloodeh is the defining mark of summer in Persian households.
The defining mark of the Grossmith brothers' Mr Pooter in The Diary of a Nobody (1892), after all, is that he is "middle class" at a time when to be middle class meant something.
