How do you know if a feedback system is positive?

Feedback system: A positive feedback loop occurs when the response causes the original stimulus to enhance. Most feedback systems are negative, because typically the system exists to maintain homeostasis, like a theromostat. The classic example of a positive feedback system is oxytocin during labor. Oxy-->increase contraction which causes more Oxy secretion-->increase contraction and more Oxy -->etc until birth.