- Engineer Grade reflective signs offer a basic level of reflectivity in completely dark conditions. Signs with Engineer Grade reflective sheeting last for at least 7 years outdoors. These standard grade signs are the most common in the US. - High IntensityGrade Reflective Signs offer up to three times more reflectance than engineer grade reflective signs. 3M's prismatic sheeting offers greater reflectance straight on but is especially bright when approached from an angle. - Diamond Grade reflective signs offer ten times the reflectivity of Engineer grade signs and come with an outdoor life of at least 12 years. These signs combine high daytime conspicuity with superior nighttime reflectivity along with wide-angle reflective performance. Diamond grade signs are the best choice for places with many visual distractions like the busy city streets.