Final answer:
Hearing a fetal heartbeat via auscultation is a positive sign of pregnancy, typically detectable from around 6 weeks of gestation.
Step-by-step explanation:
Listening to fetal heart tones is categorized as a 'positive' sign of pregnancy. Positive signs include those that are not dependent on subjective interpretation, like the presence of a fetal heartbeat that can be heard through auscultation or seen on ultrasound. A fetal heartbeat can generally be detected from around 6 weeks of gestation with a transvaginal ultrasound and sometimes later with an abdominal ultrasound.