Tower Shield Proficiency( Player's Handbook v.3.5, p. 101)
You are proficient with tower shields.
Shield Proficiency (PH) ,
You can use a tower shield and suffer only the standard penalties (see Table 7-6: Armor and Shields, page 123).
Fighters automatically have Tower Shield Proficiency as a bonus feat. They need not select it.
A character who is using a shield with which he or she is not proficient takes the shield's armor check penalty on attack rolls and on all skill checks that involve moving, including Ride.