The regulation from the Department of Transportation (DOT) on conspicuity material referred to as DOT C2 states that each trailer  of 80 or more inches overall width, and with a GVWR over 10,000 lbs. must have retro-reflective sheeting, such as reflective tape. (trailer designation comes with some additional stipulations such as date of manufacturing, etc)

All vehicles sold in the United States have factory equipped and legally required devices helping them to be visible in low light and inclement weather. However, the objective is to increase safety records of large trucks by ensuring the location and size of the trailer of large trucks is clearly seen.