OCS is dependent on the geometry and the reflectivity at a particular wavelength of an object.
Objects such as license plates on automobiles have a high optical cross section to maximize the laser return to the speed detector gun.
Optical cross section of a flat mirror with a given reflectivity at a particular wavelength
Note that the direction of the light has to be perpendicular to the mirror surface for this formula to be valid, else the return from the mirror would no longer go back to it source.
Optical cross section is not limited to reflective surfaces.