for me I just know.
Ask him lol
If they spend time talking to you or seem interested in you that is a huge sign.
Changing your screen name would be a great way to start too...
Seeing yourself as likeable through their eyes is a matter of your willingness to train your mind to first be as kind and cheerful as possible and holding fast to the belief they eventually will. If not. Their loss there are more fish in the sea and you have lots of time before you need to find someone. Just be the best you you know how to be and that ain't bad, young one.
Can you feel it, if you have face to face chats and relax in their company, then you will know. If not, you will as you get older
If they give you cold cash or presents.
Flirt with them? See what they do
I guess I'm too old.... I don't play games anymore. If I want to know if someone likes me I'd ask them out, or ask them if they're already in a relationship or some question that pertained to our getting to know each other better. If they say no, not a big deal.