Right "'" is allowed, D'oh. TANJ. But there are still others.
Who are we to say what the user should do? :-P
But no, seriously "?" would probably be used quite often, what
with the apparent trend of end users to put the file's contents in its name.
"*" in filenames might be used to either draw attention to the file,
or to make them harder to delete. If you type rmv -rf what\*ver
you don't exactly expect whatever to go bye-bye...