Cairo, Illinois, is the southernmost tip of the state of Illinois, right where the Ohio and Mississippi rivers merge together. It is the lowest elevation in the state of Illinois, and is surrounded by levees. Perhaps that is where this sign resided??
There is also a Cairo, Indiana. It is barely a blip on the map, but is in the heart of some really good farm ground in Tippecanoe county, so there could theoretically have been a dealer there...
The only "Boney" I can find is a "Boney Motor Company" in South Carolina. But I can't find a Cairo in South Carolina, except for a Cairo Middle School near Charleston, SC...
So, while this has been a fun little diversion from work over my lunch break, can't really make a clean determination on the origins of your sign or A. T. Boney in Cairo. But most likely either Indiana or Illinois, right here in the midwest.
Cheers,
JB