A November 29, 1890 item in the New York Sun titled “Whistling For the Wind”, which I discovered in Out
of Sight: The Rise of African American Popular Music, 1889-1895
:

George H. [sic] Johnson, the whistling Negro inthe Battery scene of
“The Inspector,” is a familiar figure on the North River ferryboats,
where he whistles for pennies. Eighteen years ago he went with the
Georgia Minstrels on a tour of the Old World. In Vienna they stayed
two months. While there he fell in love with a white woman. She had
no objection to his color, and they were married. Soon afterward they
came to this country, and have lived happily together ever since. A
daughter was born to them, and she has inherited the whistling
abilities of her father.

When Dramatist Wilson approached Johnson on the subject of joining
his company the whistler stuck out for a fair salary. He said that he
could pick up over $15 on the boats, and get a regular salary from a
phonograph company for whistling in their machines. Wilson had to pay
him $25 a week.

Since his engagement he has had an offer from Mrs. William K.
Vanerbilt, who wishes him to whistle for her one night after the
theater performance. Mrs. Vanderbilt will not go to a variety
theatre, but she is anxious to see all the best performers.”

I wonder about his daughter. As the years went by, how did she use her whistling? Maybe just to amaze people while she was walking down the street.

And what about his Viennese wife? What happened after she arrived in America?

NPR’s web site has a piece on him, too.