Petrus Leopoldus Franc AVG F Austriacus MDE AD Urbis Suae decus et ad incrementa artium optimarum Museum Mediceum Operibus ampliatis copiisque avctis Ordinandum et splendidiore cultu exornand curavit Anno MDCCLXXXIX

English translation: "Peter Francis Leopold of Austria AVG F MDE to honor its own capital and to increase the fine arts Museum Mediceum works enrich forces avctae arrangements and glittering ornaments adorn cured year 1789 [Google Translate]"