Interesting video from Wimp.com. The “icons” they cite as evolutionary seem to fluctuate between Batman’s chest emblem from various film/animation incarnations and the logo used on a given comics title, film poster or mini-series cover graphics. It’s not really an “evolution” of the “bat symbol” as much as a collection of different takes on it from different sources in roughly chronological order.
Sorry, can’t embed the video so click on the image or this link to see it. Nicely done, although I find it interesting the creator refuses to let you embed the video but has no problem violating U2′s copyrights for the music.