That is the name of the artist. He was Scottish.
"Dhu" is not a recognized word in English. It may be a typo or abbreviation of a longer word or phrase. Could you provide more context or clarification so I can assist you better?
From the Gaelic - it would mean the black (dhu) rock (craig).
Roderick Dhu Sutherland was born in 1862.
Roderick Dhu Sutherland died in 1915.
Dallas Dhu distillery was created in 1899.
Dallas Dhu distillery ended in 1983.
Doinall Dhu O'Connor was born in 1894.
Expedition of Dhu Qarad happened in -627.
Doinall Dhu O'Connor died in 1975.
The word for friend in Bengali is "বন্ধু" (pronounced as "bondhu").
Dhu Varren halt was created in 1969.
From the Gaelic marag-dhubh, pronounced 'mara-ghoo'"Marag dhu" refers to a traditional Scottish sausage or "pudding" which is in English is often called "Blood Pudding"The basic ingredients are Oatmeal, suet, salt, pepper and for n=marag dhu cows or pigsblood.Marag-gheal is 'white pudding/oatmeal'.