Hi. I am not sure what kind of marks you mean. Bruises? Redness? Old scars looking more prominent?
I don't know. I find bruises/scratches/minor cuts on me all the time and have no idea where they may have come from. From what you say here it seems the picture drawn and the marks are connected. Or at least your brain is finding connections there for some reason. It probably isn't coincidental.
Whatever the cause of the marks on your arm it seems clear that your body-mind is recalling or reassociating aspects of a trauma, and reassociation is a good thing (or so my T tells me - I am not sure I believe that when it is happening).