know by

know someone or something by something

to recognize someone or something by a certain characteristic. I know her by her perfume. I know this committee only by its reputation, which is not good, by the way.
See also: know
References in classic literature ?
Everybody of any consequence or notoriety in Bath was well know by name to Mrs Smith.
He told me that as he had no consecrated chapel, nor proper things for the office, I should see he would do it in a manner that I should not know by it that he was a Roman Catholic myself, if I had not known it before; and so he did; for saying only some words over to himself in Latin, which I could not understand, he poured a whole dishful of water upon the woman's head, pronouncing in French, very loud, "Mary" (which was the name her husband desired me to give her, for I was her godfather), "I baptize thee in the name of the Father, and of the Son, and of the Holy Ghost;" so that none could know anything by it what religion he was of.
We have reason to know by this time that there is no good in it and no hope, that there is nothing to be got from it but sorrow.