Another possibility is that the movement is completely unintentional. Many people have small nervous habits involving their hands. They rub their fingers together, adjust their grip, or shift their hands without thinking.
In those cases, the scratching motion may simply be part of that unconscious movement.
It can also be a playful action used during a friendly interaction. Someone who is relaxed or joking around might make the gesture without attaching any deeper meaning to it.
Context is the best clue
When trying to understand any nonverbal signal, the wider context usually matters more than the gesture itself.
Consider the situation. Was the interaction casual or professional? What was the overall body language like? Were there smiles, prolonged eye contact, or signs of nervousness?
If the gesture happens only once, it may have been accidental. If it occurs repeatedly in a similar context, it might suggest a deliberate signal.
Most importantly, pay attention to how the interaction felt. Personal comfort often provides the clearest guidance.