The Lumon Legacy of Joy is an exhibit in the Perpetuity Wing on the Severed Floor of Lumon Industries. It appears just once, in the episode In Perpetuity (37:51).
Look. Each of these is a real smile from someone on the outside. Someone Lumon Industries has helped. And they rotate these through. The true number of smiles may well be in the millions.
So what are we, like, a dental company?