You need to meet minimum reflectivity requirements and printing on engineered grade reflective might not achieve that. We always bought them and the prismatic ones are outrageously expensive.
REFLECTIVE REQUIREMENTS FOR THE REAR OF THE VEHICLE
Click to see our Reflective Pre-Made Chevron Panels
184.108.40.206 At least 50% or half of the rear-facing vertical surfaces, visible from the rear of the fire apparatus, “not including” any pump panel areas not covered by a door, shall be outfitted with retro-reflective striping in a chevron pattern sloping downward and away from the center-line of the vehicle at 45 degree angles. (see picture above)
220.127.116.11.1 Each stripe used in the chevron design shall be a single color alternating between yellow and red.
18.104.22.168.2 Each stripe shall be 6 inches (150 mm) wide.
22.214.171.124 All of the retro-reflective materials required by sections 126.96.36.199 and 188.8.131.52 shall conform to the requirements of ASTM D 4956, Standard Specification for Retro-reflective Sheeting for Traffic Control, Section 6.1.1 for Type I Sheeting. (engineer grade which is similar to what is on a car tag. The sheeting can be brighter. ie, Type 3,5,8,v92,v82)
184.108.40.206.1 All retro-reflective sheeting and materials used to satisfy the requirements of 220.127.116.11 that are colors not listed in ASTM D 4956, Section 6.1.1, shall have a minimum coefficient of retroreflection of 10 candelas with an observation angle of 0.2 degrees and entrance angle of −4 degrees.
18.104.22.168.3 Any printed or processed retroreflective film construction used to meet the requirements of 22.214.171.124 and 126.96.36.199 shall conform to the standards required of an integral colored film as specified in ASTM D 4956, Section 6.1.1.