There are so many cues in facial expressions, tone of voice, body language, etc., many cues all the time- it has to be something they see or hear, no one can read your mind. It has to be in some sort of body language or facial expression or in the phrasing of things. I think the best thing you could do for overcoming this is to master small talk. chit-chat with people, talking about simple, non-controversial things like the weather. Small talk is hugely important because it opens the door to all kinds of communication and connections with other people. I used to be so shy and I knew nothing about small talk, and it was like being trapped in a prison, seeing people connecting all around me and not being able to do this myself. It's like a form of torture, really, and getting good at small talk washes it all away. They one people are comfortable with chatting with you in small talk you can try, gradually, opening up subjects with more depth to them and connecting more with people who are open to this. Being able to go up to a stranger and have a little chit chat with them and have them start to like you because of your humor and your caring attitude(you need to care about the people you chat with at least some in order to be good at small talk) just opens up all of the social possibilities. Small talk is hugely important. If you search on youtube by "mastering small talk" you will find many videos on this subject- I would just force myself to watch at least ten of them beginning to end, if mastering they don't seem good, they may have helpful ideas further into the video, and then try their ideas in real life. This could really help you immensely, and this experience of people seeming uncomfortable around you will go away and it will be replaced by so many people warming up to you quickly- not everyone will, but the majority of people will if you would try this and really make on effort on this- just push yourself hard on mastering small talk every day for a few weeks and this will likely get so much better.