I get called Mr or Sir quite a bit by subordinates or security at our facility. It makes me feel old (I'll be 35 in Sept) but I understand it as I'm in a position of responsibility within my company. Generally after the first couple of times, I tell them they should address me by my first name.
However, I'll say this, if you're not sure, do as the military does, always append "sir" to it, and if unsure about the rank, salute the light pole.
It's like dressing up. You can never be too overdressed and you can never be too respectful. The other party will tell you how to behave around them.