Again, thinking out loud.
Use one of the warning strobes, multi colors. Place one in each area, When there is a message, have them report in by sending an SMS (email). When all emails are received, the light goes out. I probably missed the gist.
It's probably Light the strobe red for forklift operators, yellow for whatever. Light the entire city block. Each forklift operator, checks his message, and acknowledges it. When all have acknowledged, the light goes out.