question mark (?):

question mark (?) [1]: a symbol which is attached to the beginning of a linguistic form to indicate that it is doubtful; perhaps it can be said under special conditions but normally it is not heard. For example, the question mark on "?John put the book" indicates the fact that this sequence of words is not normally used as a complete clause, since it lacks any indication of where John put the book. This symbol is sometimes doubled (??) to indicate that a form is especially doubtful but not bad enough to be marked with an asterisk [1] (*). Compare exclamation point [1,2] (!). [Spanish: signo de interrogación [1]]

question mark (?) [2]: a symbol that is sometimes used as a typographical substitute for a glottal stop []. [Spanish: signo de interrogación [2]]