The Queen's Crown is treasure that can be obtained in Sly Cooper: Age of Thieves in the episode Alice in Cooperland. It is worth 267 coins and the time it takes to get to the safehouse in time is thirty seconds.
"Lo and behold, one of many duplicate crowns that the Queen of England keeps in storage in Buckingham Palace. That doesn't mean it isn't worth anything, though, as the gold, along with the owner of this crown, makes this treasure highly sought after. It's perfect for any female thief who wants to feel special."
It is located underneath of the Queen of Hearts Statue near the park's entrance. Murray is needed to obtain this treasure.