Depending what era you are trying to replicate, the text is slightly different, . . . but the dimensions are the same. See the excerpts below->
This is copied from:
TB 43-0209
COLOR, MARKING, AND CAMOUFLAGE PAINTING OF MILITARY VEHICLES,
CONSTRUCTION EQUIPMENT AND MATERIALS HANDLING EQUIPMENT
31 OCTOBER 1990
f. This paragraph applies to tactical transport
vehicles, and is intended to reduce the possibility of fuel
spillage due to fuel tank overfilling and subsequent fire
hazard, regardless of fuel type.
(1) If the fuel tank filler cap is a relief valve
type, but does not bear a warning decal reading
"Pressurized: Open Slowly," the warning note "Pressure:
Open Slowly" will be marked in 1-inch lusterless black
letters on the fuel tank near the filler pipe.
(2) On fuel tanks, where a mark would be
readily visible, measure 2 inches down from the top of
the tank and mark a 1/4 x 8-inch line, with the following
note in 1-inch lusterless black letters: "Caution: Do Not
Fill Above Line to Allow For Expansion ", Figure 20.
(3) On vehicles where a mark on the fuel tank
would not be readily visible, mark the following note in 1-
inch lusterless black letters as near as possible to the
filler pipes: "Caution: Do not Overfill--Allow for
Expansion."
And another source:
TB 43-0147
TECHNICAL BULLETIN COLOR, MARKING AND CAMOUFLAGE PATTERNS USED ON MILITARY EQUIPMENT
DECEMBER 1975
e. Excessive Fuel Tank Pressure. This paragraph
applies to tactical transport vehicles, and is intended to
reduce the possibility of fuel spillage due to fuel tank over
filling and subsequent fuel explosion, regardless of fuel
type.
(1) If the fuel tank filler cap is a relief valve
type, but does not bear a warning decal reading
"Pressurized: Open Slowly", the warning "Pressure:
Open Slowly" will be marked in 1 inch white letters on the
cap or on the fuel tank near the filler pipe.
(2) On fuel tanks, where a mark would be
readily visible, measure 2 inches down from the top of
the tank and mark a 1/4 x 8 inch line, with the following
note in 1 inch black letters: "Caution: Do Not Fill Above
This Line" . (See figure 2-1.)
(3) On vehicles where a mark on the fuel
tank would not be readily visible, mark the following note
in 1 inch black letters as near as possible to the filler
pipes: "Caution: Do Not Overfill - Allow for Expansion".