A Manifestation of Chaos: Extinction Event!
Pathfinder - Rules Clairifications - Magical and Mundane Items
(Includes Tower Shield)
It has been determined that if a character has at least a +1 Base Attack Bonus, they can use a free hand to grab a stored shield from their person and don it as a move equivalent action.
There is only one action of readying the shield to gain its AC bonus (a move action) and a move action to get the shield off (sheath) and thus lose the AC bonus (Dropping the shield is a free action). Hopefully this will not be cause for concern then, and players should not be deterred by the variety of terminology employed by the book.
Bucklers are strapped to the arm thus they require two move actions to ready. First move action to retrieve. Second move action to ready (gain the ac bonus). It also takes two move actions to loose a buckler. First move action un-straps (canceling AC bonus). Second move action stows the shield on person. You cannot drop a buckler unless it is unstrapped, if unstrapped dropping a buckler is a free action.