Checking the name

Maybe they are thinking of the function pointers in C++ vtables, where you know not just the expected signature, but the name of the virtual method that is being overridden. If you include that in the hash, you can prevent the attacker from replacing it with an unrelated function or method that happens to have the same signature.

Of course, that doesn't apply to C. But it may be possible to get a similar effect with manual annotations of some sort...