Soulmarks were a mystery. Nobody was quite sure when they started and the name 'soulmarks' wasn't official, but everyone valued them. As far as anyone could tell, they were the last words someone not biologically related to you would say to you. The lucky people got something like "I love you" or "Goodbye" or sometimes "I'm sorry". That meant that they got to say goodbye to their loved one. The unlucky people got things like "Stay safe!" or "I'll see you tomorrow!". That would mean that the loss was sudden and unexpected.
Toshiko Sato was born with three soulmarks. That wasn't exactly unusual, but most people had more. The one on Tosh's are read (in english, a language she didn't start to learn until she was eleven), "Okay?". The one on her stomach said, "It's alright. Really, Tosh, it's alright. Oh god". That one scared her parents, but not as much as the one on the back of her neck which read, "Talk to me now! C'mon Tosh!" That kind of soulmark usually indicated that the one wearing it was dying.
After the mess with the sonic probe, Tosh was at a loss as to how she'll ever meet her loved ones. So, when Captain Harkness offers her a job, she's shocked, but extraordinarily happy. Meeting Jack, Owen and later, Gwen, Tosh is amazed at all these people she loves. When Gwen demands that Tosh "Talk to me!" she's not surprised in the least and when Jack asks "Okay?" she's only mildly aware that she's going to die. It's Owen assuring her that "It's alright. Really, Tosh, it's alright" and then giving into fear and adding, "Oh god" to it that's strange to her. Tosh hadn't realized he loved her back.
Owen Harper was born with two soulmarks, an extremely low amount. Seeing this turned his mother against him, making her think he would never be loved, regardless of what they each said. The one on his stomach read, "Owen!" and Owen would often trace it through his shirt, wondering about who would say his name in alarm like that. The one on his upper thigh, however, amazed him. After all the neglect and abuse from his mother, he really wanted to meet the person whose last words to him would be "I love you".
Years later, Owen met Katie Russell, whose "Good luck" soulmark was in the same place as his "I love you". They bonded over coffee and cheesy movies. Owen had hoped that it would be a long while before those words were spoken, but he had no such luck. Katie would die on the operating table, along with all the doctors in the room, her last words whispered to Owen only moments before entering the room. Toshiko Sato was a first a slightly timid woman who slightly annoyed Owen, but over time, he grew to love her and as radiation filled the room, Owen wasn't the slightest bit suprised to hear "Owen!" come out of her mouth.
Ianto Jones had three soulmarks. One said "We can be upgraded together",which had confused him for years until the Battle of Canary Wharf happened, and even afterwards, he refuses to acknowledge what he knew was coming. The second was even more confusing and he used to spend long amounts of time wondering what circumstances would bring it about. It read "Rerouted the blast, couldn't save him". This was explained when Tosh died in front of him and it felt like getting shot through the chest. The third and last one read, "Yes, I will. I promise, I will", which had always seemed like the answer to a question that Ianto had asked, so he didn't expect to understand it until it happened, which it did, with Jack as Ianto lay dying in his arms.
And Jack? Well, Jack had so many soulmarks that you couldn't see his skin in some places. His parents had been shocked and so had all of the Boeshane Peninsula, but in the end, they'd taken it to mean that he would love much and be loved in return.