In TDK Returns, the chest emblem is a protective plate. They explain the yellow oval is to make it a target so he gets shot less elsewhere.
The armor concept is something that developed slowly, bit by bit, onto Batman over time, but -really- gained major appeal thanks to Tim Burton, with influence from Frank Miller.
Obviously, Nolan cranked that up to the next level. It's a self-improving franchise, bounces ideas off of itself through various mediums and series.