You were sitting on Castiel's lap, you were staying at his apartment for the night.

"Darling?" Castiel spoke after a few moments. "Can I borrow your hand for a second?" He asked, looking down at you with an innocent smile. Of course, you nodded and held your hand out for him. He quickly held your hand, grasping onto your wrist, you felt Castiel writing on your wrist with a pen..

...

You glanced at what he was writing on your wrist, it said 'Castiel's property'..