Sorry for pedantry, but that would be cum signo interrogationis ('cum'+ablative case, 'interrogationis' in genitive).cum signum interrogatione
Well, that does not mean ''with a question mark'' in Latin...cum signum interogatione (with one r).
... the same goes for c.s.i. = cum signum interogatione for medical purposes. So maybe our physicians don't care too much about correct Latin .if you google it, you'll find many examples