The letters on glasses lenses are usually invisible marks of lenses, which are also the brand's anti-counterfeiting standards, and can only be seen in the case of fog.

Some signs are R, indicating the right eye; Some signs are l, which means left eye; Some labels are C, which means cylindrical lens (astigmatism lens); Some labels are S, which means spherical lens (myopia lens or hyperopia lens); Some labels are P, indicating progressive multifocal lenses; Some labels are D, indicating luminosity (for example,-1.00D is commonly known as 100 degree myopia lens); Some marks are BC, indicating the axial direction of astigmatism; Some labels are AX, indicating the axial direction of the prism; Some marks are dotted, indicating the position of spot welding.