JK, it's not a 30.06 sign, but another using a 2x.xx. I wish I could recall the exact verbage, but I'll be sure to get more info next time...assuming someone doesn't beat me to it first.
If i'm not mistaken, the lettering on the 30.06 sign has to be one inch, black on white. Don't recall the verbiage.
Here it is;
Texas Department of Public Safety - Courtesy, Service, Protection