What did Marguerite discover in Sir Percy's office? To what did all of the clues point?

Marguerite found a ring in her husband's office. All clues pointed to the fact that her husband just might be the Pimpernel.

She stooped to pick it up. It was a solid gold ring, with a flat shield, on which was engraved a small device.

Marguerite turned it over in her fingers, and then studied the engraving on the shield. It represented a small star-shaped flower, of a shape she had seen so distinctly twice before: once at the opera, and once at Lord Grenville's ball.