I believe that it means that the girl when she was wearing her clothes she was respectful and when she started to get naked she became lower and lower and smaller

Well as you can see in the end of the poster there is a company name: ArtFoco Optica which is probably an eye clinic or something similar. And I dont know if you were in for a check in an eye clinic but when they check your eyes they show you a poster with letters from the biggest ones to the smallest ones. So that should explain this ad