Leonardo Di Vinci print mark help

I know this is a Leonardo Di Vinci Virgin Mary print but has anybody seen this mark? It is a W with a crown over it in a circle. Any help would be great. Thanks everybody!!

 

Maybe?


http://www.metmuseum.org/toah/works-of-art/51.90

 

O ok I see... it was actually on the original art, I thought that was a printers mark.

 

I think the mark involves the royal Windsor something or other. There's mention of it in the text...

" Further preparatory studies for the Virgin and Child with Saint Anne composition are at the Royal Library (Windsor Castle), and these transform scientific principles into a pictorial language of magical force and nuance."