425 ILCS 68/20
(a) The truss construction emblem shall have a bright and reflective color or be made of reflective material. The shape of the emblem shall be an isosceles triangle and the size shall be 12 inches horizontally by 6 inches vertically. The following letters shall be printed on the emblem in a conspicuous size and color:
"F" to signify a floor with truss construction;
"R" to signify a roof with truss construction; and
"F/R" to signify both a floor and roof with truss construction.
(Source: P.A. 90-434, eff. 8-16-97.)