I'm applying to PhD programs and I've gotten in touch with a couple of prospective faculty. If they sign their emails with their first name, is it good to assume that they're okay with being called by their first name? Or should I play it safe and wait until they invite me to do so? Or should I simply ask? I don't want to come off as disrespectful, but I don't want to be regarded as not being able to take a hint either. I have a master's degree and know at a LOT of, if not most, grad students call their professors by their first name. I've never been able to really do so, and half the time I actually end up avoiding their names altogether, which I know is the worst of the worst of ideas because it comes off as more disrespectful than simply using their first names, but I for some reason can't get over the mental barrier of not being able to call them anything unless they tell me on the first day what they want to be called. Any advice?