There were a number of variants of the 'AC' badge, used on vehicles and for advertising, starting circa 1907 when the AC logo was introduced. Nearly all have the familiar AC script at the heart of the badge, but even that has varied in detail.
One very early example, from 1909, is shown on page 16 of the May 2010 ACtion, another circa 1911 on page 12 of the June 2010 Action.
For later cars, Hawk 289 has it about right. From my hazy recollection, the earliest 260 Cobras had the familiar solid aluminium AC roundal fitted on the bonnet - which was removed in America! The pedals survived though!
Re the 3000ME, the larger script badge, fitted to the grille and boot lid, has an F&S Part Number 63752/SF visible when viewed from the underside. Are the AC 289 Sports, AC 428, and other similar badges, likewise identified?
Across all badges, there are too some subtle differences in apparently similar badges, to accomodate the body curvature of each model and also front-to-rear.
I am slowly gathering detailed information for an ACtion Archive article, probably some time in 2011 - but don't hold your breath!