A Hazardous Materials Table entry has the symbol "A" in Column 1. What does this indicate?

AAMVA CDL Manual, Section 9.3.3 (nhcdm.pdf p. 9-4); 49 CFR 172.101(b)

A driver hauling a load by truck who sees an "A" symbol on the shipping paper needs to understand that symbol describes an air-transport-only regulatory trigger — it does not mean the highway shipment is exempt from all other hazmat rules that otherwise apply to that material.