49 CFR §172.544

1. (a)Except for size and color, the COMBUSTIBLE placard must be as follows:
2. (b)In addition to complying with § 172.519, the background color on the COMBUSTIBLE placard must be red. The symbol, text, class number and inner border must be white. On a COMBUSTIBLE placard with a white bottom as prescribed by § 172.332(c)(4), the class number must be red or black.
3. (c)The words “FUEL OIL” may be used in place of the word “COMBUSTIBLE” on a placard that is displayed on a cargo tank or portable tank being used to transport by highway fuel oil that is not classed as a flammable liquid. The words “FUEL OIL” must be white.