This is the 5693rd most frequent Russian word.
признак
"Признак" - sign, feature, characteristic, or symptom.
Here, 'признак' is used to denote an observable indication of a season.
Признак осени — это опадающие листья.
A sign of autumn is the falling leaves.
In this sentence, 'признак' refers to a characteristic or evidence of a condition.
У него был признак умственной активности.
He showed signs of mental activity.
'Признак' here signifies a defining feature or mark of a current trend.