As many auto shops in California offer emissions testing, smog check signs are essential for advertising this important service. Smog check signs to notify drivers that your shop is a certified testing station, which can attract traffic from car owners requiring compliance testing. Smog check signs can be attached to the building, set as a freestanding sign, or even used as a window decal, but they need to be bold and easy to spot from the street. Reflective or lighted versions offer visibility during early morning and late evening business hours.