Maybe I don’t mean what you mean.
‘’ two single quotes are not syntactically valid, so you could use that convention. You can just make up your own convention.
Either way, better a key that can be pressed than one that can’t, IMHO. 
How about a user can define their own code/quote/etc delimiters?
I was more thinking of using the forum as a user… If I am a user of a forum which utilises this feature, can I disable it on my account/profile?