A- Every scar someone gets on their body will be seen on their soulmate; the scars start to appear around the age of five. The soulmate doesn't feel the pain of the scar as it just seems when their partner gets it.
Or
B- At the age of 10, you get a name on your wrist; this name can either be your Soulmate or mortal enemy. You know who they are as the names will glow once you are 50 yards from the person; the closer you get, the brighter the glow.
Or
C-Red string is connected to your pinky. Only you and your soulmate can see this string; the red string will never disappear unless the Soulmate is killed. There is a chance for a new string to appear, but like most, the red string tieds into a knot to never be unwoven.
