Mayor Bloomberg was ready yesterday when it came time to sign the official oath of office for his third term.

Standing at a City Hall desk labeled as belonging to George Washington, the billionaire mayor who spent $102 million to get re-elected, reached into a pocket, pulled out his wallet and began counting out dollar bills.

When he got to $9 — the administrative fee — he handed over the sum to City Clerk Mike McSweeney.

Today, he’ll take the oath of office again at a ceremonial inaugural outside City Hall.