sixxon:

Tattoos or Marks

• Red tallies appear for every person you’ve loved, black for every person you’ve loved that has died, and a white tally for when you meet your soulmate
• A mark that matches, sometimes like a puzzle piece to someone else, and grows hotter the closer they are to you
• You have a tattoo of what your soulmate is most passionate about
• You have a tattoo of the first words they say to you
• You have a tattoo of how old you both are when you meet
• Changing tattoo that tells you the coordinates of where your soulmate is
• Tree tattoo that changes with the seasons, but blooms pink in spring instead of white if you met your soulmate
• Identical tattoos or birthmarks
• Incomplete tattoos that complete themselves on your skin when you meet the person with the rest of your tattoo
• Tattoos that change colour depending on what your soulmate is feeling

Eyes

• Heterochromia – you have one eye of your soulmates eye colour and when you meet you get your own eye colour instead of having two different eye colours.
• You only see in black and white until you meet your soulmate
• Reverse black and white where you give up seeing colour when you meet your soulmate
• You only see in black and white until you touch your soulmate
• You only see in the different shades of your soulmates eye colour until you meet them
• You can’t see the colour of your soulmates eye colour until you meet them
• You see colour the first time you hear your soulmates voice directly and the colour spills from their lips

Ears

• You can hear your soulmates voice in your head, but only when they sing
• The secondary voice in your head is your soulmate speaking
• You can speak once you meet your soulmate
• You can hear once you meet your soulmate (the first thing you hear is their voice)

Time & Age

• When you reach 18 you stop aging until you meet your soulmate
• Watch countdown to when you’ll meet your soulmate
• Reverse countdown, your clock counts up and freezes when you meet
• You have a clock on your body that tells you what time it is where your soulmate is, it changes colour when they get closer to you

Body or Hair

• At new years on midnight for a single minute you possess your soulmates body
• Your chest glows when you look them in the eyes
• Marks on your soulmate appear on your own body
• You have your soulmate’s hair colour on a stripe at your wrist, when they dye or chance their hair colour the stripe changes
• If you change your hair colour, your soulmates changes to the same colour (your hair goes to it’s natural colour when your soulmates does)
• When you change your hair colour, your soulmates eyes change to that colour
• You and your soulmate share all physical senses (I.E pain, heat, pleasure, etc…)

Other

• Red sting to connect soulmates
• Your soulmate is the only person you remember from your past life
• Everyone is given a journal that they can use to write to their soulmate
• When you sleep, if your soulmate is awake you can see what they’re doing
• You dream your soulmate, but very basically (such as their silhouette or the view of their back) 
• Telepathy soulmates
• Sharing skills and talents with your soulmate
• When your soulmate eats something you crave what they’re eating
• When your soulmate cries you cry
• When you kiss your soulmate for the first time your entire body glows

I got a lot of ideas from this post so I recommend you check that one out too!

Common AU Masterlist Link