• Signoria was an abstract noun meaning (roughly): government; governing authority; de facto sovereignty; lordship' in many of the Italian city states during the medieval and renaissance periods.
• There is also Piazza della Signoria that is an L-shaped square in Florence, Italy.

The statue of David is in the Academia in Florence, Italy. A replica stands outside as you enter the city of Florence. There are many other statues carved by Michelangelo.

It's not a painting but a sculpture, the original is housed in the Accademia Gallery in Florence, where it attracts many visitors. A replica is on display in the Piazza della Signoria, Florence, Italy.

Niccolo Machiavelli was buried in the church of Santa Croce in Florence, Italy. His tomb is located in the Basilica di Santa Croce, which is also the final resting place for other notable figures such as Michelangelo and Galileo.

Yes, they were commisioned by the Signoria of Florence to paint the Grand Council Chamber in the Palazzo Vecchio; Leonardo worked on the Battle of Anghiari and Michelangelo on the the Battle of Cascina