Question:
It is known that we are forbidden to write (with our finger) on a window on Shabbos, etc. May, however, one touch the window, etc. or put his hand on it even though this will cause a mark to be left?
Answer:
If the person does not have any intention to write on the foggy window or dusty book one can touch them on Shabbos
Sources:
Gemorah Shabbos 22a, Rambam Shabbos 1:5, O:CH 337:1
