Signals are a good suggestion only if the roommate listens.
My roommate issues were solved fairly quickly. After the first time the issue was brought up, I simply made a call about two hours in advance to a horny friend of mine with a serious thing for Asian guys. By the time I wanted "a little privacy" she'd dragged his ass back to her dorm room - and I didn't see him again for the next three days.
He bought me a 40 of vodka later on that week.
