The phrase "as the hallmark" is correct and usable in written English.
It can be used to indicate a distinguishing feature or characteristic of something, often implying a standard of quality.
Example: "Her dedication to her work is recognized as the hallmark of her success in the industry."
Alternatives: "as the signature" or "as the defining characteristic".
Tolstoy's preference for particularities over abstractions is often described as the hallmark of his thought.
Field research was established as the hallmark of all the branches of anthropology.
After all, Ken Clarke asserted it as "the hallmark of a civilised society" even as he implemented his cuts package.
However, the connection with Mr. Roh, who had billed transparency as the hallmark of his 2003-08 term, caused an uproar.
If "freedom" is the word Bush and Cheney want as the hallmark of their administration, they should begin with freedom of information.
Fast, reliable methods of search and retrieval are sometimes identified as the hallmark of our information age; "Search is everything" has become a proverb.
Above all, the NIC identifies scarcity - of land, water, oil and food, and, especially, "airspace" for carbon emissions - as the hallmark of tomorrow's world.
But critics say China's state-run education system — promoted as the hallmark of Communist meritocracy — is being overrun by bribery and cronyism.
In the diversity of her talents and interests, she exhibited the universality that has been regarded as the hallmark of the German Romantic spirit.
"Not just a 'gingerbread' saint or a 'holy card' saint but a modern-day devoted daughter of the Church" whose work on behalf of the poor stands as "the hallmark of her life".
But all the subjects now regarded as the hallmark of his oeuvre, even the racial undercurrents that people in this supposedly colorblind society have always been reluctant to acknowledge, are on display in "The Woman Without Sin".
