From the Super Mario Wiki
The Pearl Necklace is an item in the SNES and PC releases of Mario's Time Machine. It is made up of many small pearls. In Mario's Time Machine, Francis Drake gives it to Mario after Mario asks to have an audience with Queen Elizabeth I. To prove that Mario has the trust of Francis, he gives Mario the Pearl Necklace and tells him to show them to one of the queen's handmaidens. By showing the necklace to the handmaiden, she can guarantee an audience with the queen, according to Francis. Once Mario brings the Pearl Necklace to the handmaiden, she recognizes that he has the trust of Francis and assures Mario that the queen is now able to see him in the throne room. Despite saying this, Queen Elizabeth only speaks to Mario after the history pages are filled out with the information Mario gains by talking to various people.