Best Way to Grab an Invigilators attention?

Say you need more paper and time is marks, but they don't notice you, you can't exactly shout across the hall to turn the hell around. Usually I keep working with my hand up on something else, but say its the last 5 minutes and you've had a breakthrough with the last tough question, but you've scribbled the entire page with a previous failed attempt, what do you do?