The general consensus among fans is that the Autobot insignia was based on G1 Prowl/Bluestreak's head, and the Decepticon logo was based on Soundwave's. Anyway, here's a quick comparison pic...


As far as canon is concerned, the Autobot insignia is based on the image of Primus, while the Decepticon logo is based on Megatronus, a.k.a. The Fallen.