Sergeant Brown was well-known in St. Augustine at the turn of the 20th century. We know a lot about him through his book, Ponce de Leon Land and Florida War Record. This photo and attached biography come from this book which can be read at Google Books.
A quick search in Ancestry.com finds SGT Brown and his family living here in 1910 in one of the post quarters that still exist on the grounds of the Florida National Guard headquarters, right next to the National Cemetery he tended for years and where he now lays at rest. After his death, Mary and their daughter, Mary Ethel, moved to Saratoga, New York. When Mary died in 1928, she was reunited with her husband here at the cemetery.