Yeah, I have seen a few with the boing ball logo, as well. (There was a company that was selling those boing ball square logos as new/old stock, as well, to replace the checkmark a few years back)
As I understand it, the boingball was on the first run of North American A1000s. Then subsequent runs had the Checkmark. The C= logo was either a prototype or perhaps a non-North American release.
The Checkmark logo is the most common, then the boingball, then the most rare C= logo. At least that's the way it is in the US.
