ATK...and MoDot

I emailed the following letter to the Missouri Department of Transportation:

Everyday when I am driving into work, I see on the back of signs the letters "ATK" spray painted on the back. What does this mean? It is driving me insane! I see this most frequently on 270 between Olive and 40.

Your timely response is greatly appreciated.

Their reply:

Dear Mr. Wilson,
Thank you for your email. The spray-painted initials on the backs of our temporary construction signs belong to our signing subcontractor, ATK. With so many signs around, they paint their initials on the ones they place around the work zones to keep track of them. Mystery solved!
Eve E. Jost
MoDOT Customer Service Representative