The Steed is one of The Warrior, and her season is Mid Year. Those born under the sign of the Steed are impatient and are always hurrying from one place to another.
The Steed ability grants a bonus of 20 to your Speed attribute.
This is useful for thieves. It is also good if you are an Oblivion veteran and want a challenge without birthsign bonuses that help you fight, as getting around faster still means winning faster.