It nice of the writer of this sign to set a puzzle to entertain us as we shop.
If it's about one umbrella, we're left wondering what the umbrella possesses.
Perhaps the umbrella's handle was $19.99. Or maybe its spokes.
On the other hand, if there's a 'typo' and the sign is advertising umbrellas, we're left wondering what other single item used to be $19.99 and is now $9.99.
What a mystery.