It is found that some women scratch the shoulders or the back of a man during an intense session of intercourse. Some women practice it as it becomes a habit for her, and some do when the intensity of pleasure hit the ceiling.
Some men, new to witness such behavior may perceive the woman as a psycho and some men may take is the signal of satisfaction in bed.
There may be many random reasons behind that act to scratch or never scratch.
Expression of arousal
Could be expression of enjoyment /satisfaction, forget the pain and feel proud instead
Excitement after a long gap
It may be out of love, as she has excited to touch you after a long wait
Some women don’t intentionally scratch. It could happen by accident.
Marking you as her Personal belonging
Some women want to leave a mark on a man to just signify that the man is her property, just like kids writing their names on walls or objects with that objective.
To get into you deeply
During an intense love making session, some women do it as symbolical way of expressing the desire to go deep into the partner.
Act of revenge
If she is scratching till you bleed during intercourse, it may be an act of taking revenge in a clever way.
To turn her On
Some women gets satisfaction from the act and turned on only when they are allowed to do certain things