In Spanish I would say to member @cmartinez : César, ¿no tendríamos que verificar cuidadosamente la propuesta del miembro bogosort, antes de dar una respuesta? Here, we need the opening question mark.A prefix symbol for interrogative statements in English is redundant, as most questions include question words early in their development that signify the intent. "How are you doing?" "Hey, what are we eating tonight?" etc.
In more complex sentence constructions, our brains naturally build bite-sized chunks of information as they parse the sentence. The question chunk almost always comes at the end, which fits well with a postfix symbol, as it associates the grammatical signifier in proximity with the information of the question. "Honey, I know how much you love banana bread (you mentioned it in our wedding vows), and I know I said that you could have the last bite, but -- pretty please with a cherry on top -- can I have the last bite?" Reading that sentence, the brain builds a cogent picture in tempo with the words; a prefix '?' symbol wouldn't add anything or aid in parsing.
Note also that, in English speech, questions are typically indicated by a rising inflection at the end of the statement, perfectly in line with a question mark at the end of a sentence.
Otherwise, we move that question mark to the end, like this: César, tendríamos que verificar cuidadosamente la propuesta del miembro bogosort antes de dar una respuesta, ¿no?
