Ill. Admin. Code tit. 92 § 554.419
The "OVERSIZE LOAD" sign should have approximately 12-inch black letters with a 2-inch stroke on a yellow sign that is approximately 7 feet wide by 18 inches high. The minimum letter size is a height of 10 inches with a stroke of 1.41 inches. The signs are mandatory on escort vehicles and on the front and rear of vehicles and loads over 10 feet wide, 14 feet 6 inches high, or 75 feet long. When an escort vehicle is traveling ahead of the permit load, the sign shall be visibly displayed toward the front, and when the escort vehicle is trailing, the sign shall be displayed toward the rear. The sign on an escort vehicle may be reduced to include 8-inch-high letters on a panel that is 5 feet wide by 12 inches high.
Ill. Admin. Code tit. 92, § 554.419
Amended at 11 Ill. Reg. 3248, effective February 3, 1987