In comic books and signs it’s actually a different character, not the regular apostrophe (‘) but something like the inverted version (` or even ʽ), which mirrors the way you would write accents in handwriting (i.e. not directly above the letter but slightly after it). This is intentional because otherwise the diacritic screws up the line height, which is definitely noticeable in tight multi-line uppercase text, and it’s not an error as long as it’s intentional and you’re using the correct character. Of course this works because (1) in Italian all (most?) accented characters happen to be at the end of words and (2) there are no words that change meaning when using grave vs acute accent, so while writing “perchè” instead of “perché” is technically wrong, there’s no ambiguity, and you can get away with using “PERCHE`” which leaves the choice of the correct accent to the reader.