See https://books.google.com/books?id=jRhA-s7F8XUC&pg=PR10&lpg=PR10&dq=manuscript+symbol+for+sols+sous&source=bl&ots=fCIC9TZwD8&sig=ACfU3U2nZazwEWc7VF-5YdMu-xsFnWpTvg&hl=en&ppis=e&sa=X&ved=2ahUKEwjztKKkoHnAhXhg-AKHY5kAn4Q6AEwCnoECAsQAQ#v=onepage&q=manuscript%20symbol%20for%20sols%20sous&f=false @thuchacz and @njr2128
editorial comment for this exists and was left very vague - perhaps more research can shed more light on this