It is a bit late now to respond, but I couldn't resist having a look in here because I love the title of this thread.
Of course letters are a metaphors of the very thing they try to communicate i.e. the a communicating a-ness.
But then when we know its an 'a', then what kind of 'a' is it?
Is it a kind a or an aggressive a, what did it have for breakfast?
It becomes very Type CSI.
Interesting.

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Michael Hernan

Ehses, H., Lupton, E. (1988). Design papers 5. Rhetorical handbook: an illustrated manual for graphic designers. NSCAD University. Halifax, Nova Scotia, Canada.