Until recently, I attached only one figurative meaning to the word hallmark:
A distinctive mark or token of genuineness, good breeding, or excellence.
Here are some examples of the word used in the sense of a trait that denotes admirable excellence:
The hallmark of a scholar is attention to detail.
Indeed, if style, grace, intellect, and capacity for rebirth are the hallmarks of [a Renaissance woman], then Lois Wilson qualified in every sense.
The hallmark of an honest politician is an innate understanding that their most sacred duty is to fulfill the responsibilities of their office.
Emotional intelligence is the hallmark of a good leader.
Osbeck also noted a fourth writing trait—elegance—which he describes as the “hallmark of great legal writing.”
Rereading, editing, and revising the initial draft into a good paper are the hallmarks of good writing.
In each of these examples, the idea of excellence is implicit in the word hallmark. This connotation of excellence derives from the word’s literal meaning: “a mark or device placed or stamped upon an article of trade to indicate origin, purity, or genuineness.”
The practice of placing marks of origin and authenticity on products made of gold or silver dates to the early Middle Ages. One such mark in England was a leopard’s head. In the 15th century, when a law required all goldsmiths to bring their wares to Goldsmiths’ Hall in London to be marked, the identifying device came to be known as a hallmark.
Hallmark seems to have retained its connotation of quality and excellence until the 20th century.
For example, the Hallmark Greeting Card Company was founded in 1910. Founder Joyce Clyde Hall felt that greeting cards “represented class.” Playing on the founder’s name and the goldsmith’s mark of excellence, the company adopted the name Hallmark in 1928.
By midcentury, however, writers had begun using the word absent its connotation of worthiness:
Do you know the hallmark of a second rater? It’s resentment of another man’s achievement.—Ayn Rand, Atlas Shrugged (1957).
Writers familiar with the word’s positive associations continue to use it to denote excellence. For others, hallmark has devolved into a mere synonym for trait or “distinguishing characteristic”:
Ruthlessness, deception and devious behavior is [sic] the hallmark of the successful politician.
Expression of multiple horizontally acquired genes is a hallmark of both vertebrate and invertebrate genomes.
A Hallmark of Alzheimer’s Can Show Up in Young People Too
There’s even evidence that some speakers aren’t too sure that hallmark means trait:
Many researchers have also theorized that a lack of self-awareness is a hallmark trait of narcissists.
Writers who prefer to reserve hallmark to denote “proof of excellence,” may choose from the following list for words to convey the idea of trait or characteristic: