Hi Charles,
Some more sources for you from my Belknap file:
These books had stuff on Jackson Belknap:
Mobile: Fact and Tradition - Erwin Craighead (1930) - see pages 346-347
From Mobile's Past - Erwin Craighead (1925) - see page2 90-92
Craighead's Mobile - Caldwell Delaney (1968) - see page 191
Belknap has an obit in both Mobile newspapers of February 10, 1917. He was 92 when he passed. His wife Sarah died on Sept. 6, 1917. The family cemetery plot is at Magnolia Cemetery in Mobile, Square 12.
The earliest newspaper ad I have found for making military flags is in the Montgomery Mail of November 17, 1860. Besides the large ad there is a short article plugging his business.
The Mobile City Directory before and right after the war lists him as a sign painter and related but later issues state he had the Mobile Advertising Company (1880) and by 1892 was listed as an inventor.
Hope these help.
greg Biggs