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?
If the person does not have any intention to write on the foggy window or dusty book one can touch them on Shabbos
Gemorah Shabbos 22a, Rambam Shabbos 1:5, O:CH 337:1