Hi David, 
 
I'm not sure I've ever seen one, but I know that Burton railed against the "yataghan-bayonets" of the French in the 19th Century.  In theory it sounds like a horrible design.  In practice, I don't know. 
 
Similarly, a saw-backed bayonet is kind of missing the point.  The teeth will catch on anything you stab it into, so either it's not a functional bayonet or not a good saw. 
 
Best, 
 
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