This Wednesday the Public Authorities Control Board is likely to determine the fate of the large Atlantic Yards project. Lost in the great debate about the existence of this development is a second important issue: the developer’s plan for immense signs to mark the presence of the Nets arena. The signs would rise as high as 150 feet, equivalent to 15 stories, and extend for 75 feet along each of Atlantic and Flatbush avenues. They would be illuminated and could display moving images. This would greatly affect both the arena’s neighbors and the general public.