The Lumon Legacy of Joy is an exhibit in the Perpetuity Wing on the SVR’D Floor of Lumon Industries. It appears just one, in the episode In Perpetuity (37:51).

It is not called the “Smile Wall.”

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.
— Irv

So what are we, like, a dental company?
— Helly