Sorry to disappoint you all, but PWS means Part Worn, Serviceable. It is used on clothing that has been handed back into stores and is suitable for re-issue. It is still in use in the RAF today. Clothing marked as such is usually issued for "second line" use, such as in the cadet forces. During the war, any item deemed suitable for re issue would have been stamped, although it seems more common on War Service Dress, possibly because of the "workwear" nature of it.