Hello padron. I am the editor here, been investigating paranormal activity basically all my life (my parents are investigator, kinda grew up around it). The only time I have seen with my own eyes this happening is during a channeling event or when a spirit has entered the body of someone. The one that stands out the most to me is when we were in the presence of someone channeling, they couldn't speak a clear language anyone of us could comprehend. The spirit was asked repeatedly "what is your name?" When verbal communication wouldn't work, the spirit "raised" their name on the forearms of the person. It was a purplish color, kindof like when you get a bruise. It stayed on her arms for almost a week. As far as waking up with it on your arms, I haven't encountered anything like it before but like you said, there are documented cases of it.