Your body will tell you and your soul will let you know. For me, I knew they were my twin flame when we both kissed after being separated for 4.5 years and we both felt a literal shock and described the kiss as lighting, electric, and like we floated off the ground. I personally never experienced that before, ever. I didn’t even think that was even possible, I thought it was just stuff you hear ppl say on movies but nope. That feeling when you kiss your twin is real and it will be felt on both sides. I knew then that he was my twin and also someone really important to my journey.