A method of producing an optical element having a mark, which is substantially unobservable when a source of electromagnetic energy is viewed through the optical element at a first position that has a first alignment with the mark and which is substantially observable when said source of electromagnetic energy is viewed through said optical element at a second position that has a second alignment with the mark, comprising: (a) irradiating at least a portion of a surface of said optical element with laser radiation, thereby forming a plurality of elongated grooves in said portion of said surface, wherein, each elongated groove has a longitudinal axis, each elongated groove is substantially parallel to an adjacent elongated groove, the longitudinal axis of each elongated groove is aligned substantially parallel with a common longitudinal direction that extends from a center point of said plurality of elongated grooves, each elongated groove independently has a depth of from 0.1 micrometers to 2 micrometers and a width of from 10 micrometers to 60 micrometers, and said plurality of elongated grooves together define said mark; and (b) forming a clear film over at least said portion of said surface and said plurality of elongated grooves, wherein the portion of said surface has a first refractive index, and said clear film has a second refractive index, and a difference between said first refractive index and said second refractive index has an absolute value of from 0.01 to 1.2, and wherein, said first position has a first alignment with said center point that is substantially parallel to said common longitudinal direction, and said second position has a second alignment with said center point that is substantially orthogonal to said common longitudinal direction. (a) irradiating at least a portion of a surface of said optical element with laser radiation, thereby forming a plurality of elongated grooves in said portion of said surface, wherein, each elongated groove has a longitudinal axis, each elongated groove is substantially parallel to an adjacent elongated groove, the longitudinal axis of each elongated groove is aligned substantially parallel with a common longitudinal direction that extends from a center point of said plurality of elongated grooves, each elongated groove independently has a depth of from 0.1 micrometers to 2 micrometers and a width of from 10 micrometers to 60 micrometers, and said plurality of elongated grooves together define said mark; and each elongated groove has a longitudinal axis, each elongated groove is substantially parallel to an adjacent elongated groove, the longitudinal axis of each elongated groove is aligned substantially parallel with a common longitudinal direction that extends from a center point of said plurality of elongated grooves, each elongated groove independently has a depth of from 0.1 micrometers to 2 micrometers and a width of from 10 micrometers to 60 micrometers, and said plurality of elongated grooves together define said mark; and (b) forming a clear film over at least said portion of said surface and said plurality of elongated grooves, wherein the portion of said surface has a first refractive index, and said clear film has a second refractive index, and a difference between said first refractive index and said second refractive index has an absolute value of from 0.01 to 1.2, and wherein, said first position has a first alignment with said center point that is substantially parallel to said common longitudinal direction, and said second position has a second alignment with said center point that is substantially orthogonal to said common longitudinal direction. said first position has a first alignment with said center point that is substantially parallel to said common longitudinal direction, and said second position has a second alignment with said center point that is substantially orthogonal to said common longitudinal direction. <EOS>