Pope Leo X is a very significant historical figure who was Pope from 1513-1521.
The year is legible (1506) and the signature is complete.
According to Saggiori’s book, the jo.(for john) is preceded by a” v.r.” (I would say the v .stands for vescovus or vice chancellier)
Here the initials before the j.o. stand for something else, but they are indeed present and fully legible.