I was under the impression that the Boing ball was never an official commodore logo. Seems to me that one would be safe.
The boing ball (as used by Amiga, Inc., in both color and stippled black and white) is an active registered trademark in the US. The classic logos should all be fair game, but the "Amiga" trademark is still owned by Amiga, Inc. for use in personal computer products, forums (yes, forums are specified), etc.
