What does this highway sign mean?

[The Chao Goes Mu]

I was driving along I-90 between Buffalo, Ny and Cleveland, OH when I say these signs along the highway and I have no clue as to what they mean.

The sign looks like a "NO PARKING" sign except instead of a "P"
with the red slash of forboding there are the letters "HC"
What is this "HC" and why is it forbidden?

Help before I yank out my hair!

Thanks!

C

[Athena]

IIRC, HC = highly combustible. I've seen these signs before tunnels where trucks carrying combustible materials are not permitted to enter.

[toadspittle]

No Hazardous Cargo.

[Q.E.D.]

I believe it means No Hazardous Cargo.

[Ice Wolf]

From here (http://www.gribblenation.com/ohpics/gallery/):

No 'HC' and 'HC' signs are comon practice in Ohio cities prohibiting or allowing trucks with hazardous materials on specific highways.

Stands for "Hazardous Chemicals".

[Ice Wolf]

*sigh* Or "Hazardous Cargo". Sorry, I'm posting while waiting to catch a plane home. :)