Needs review
Source: Player's Handbook

Description: You are proficient with bucklers, small shields, and large shields.

Prerequisites:

Required for: Improved Shield Bash, Stoneback, Tower Shield Proficiency

You can use a shield (barring tower and exotic shields) and take only the standard penalties.

Special

Several classes such as barbarians, bards, clerics, druids, fighters, paladins, and rangers automatically have Shield Proficiency as a bonus feat. They need not select it.

Normal

When you are using a shield with which you are not proficient, you take the shield's armor check penalty on attack rolls and on all skill checks that involve moving, including Ride checks.