Positive signs include audience members leaning forward and listening to what you say. They nod their heads in agreement. They make eye contact with you. They look at your slides.
Negative signs include closed body language: Audience members lean back in their chairs and fold their arms across their chests. They glance at their watches. (Some may check to see if their eyes are still running.) They look around the room. The negative signs mean you need to change your approach or your delivery. Perhaps the best way is to pause and ask your audience for direct feedback: “I get you’re not comfortable with this discussion. What are your concerns?” Better to address the issues than ignore them.