Sweaters on chairs

One blog I always read is Librarian etiquette. It reminds me of some of the issues I have experienced as a librarian. For many years I was the computer guy on staff. Often I'd have to go from desk to desk testing something or fixing something. Inevitably I'd face the dilemma of what to do when the chair in front of the computer had a sweater draped around it.

I suspect this is a female thing. Men, to my knowledge, never wrap sweaters around their chairs. I suppose it makes the desk seem more cozy or is a way of establishing territorial rights to the chair.

The problem occurs when someone else needs to sit in the chair. I never know the proper thing to do in the situation.

Should I stand instead of sit because there is a sweater on the chair? Can I tactfully remove the sweater? Should I try to find another chair and move it over? Can I sit on the sweatered chair leaning forward so as not to touch the sweater?

When librarians go on vacation why do they always leave their sweaters on their chairs?