Maybe very late 40's - early 50's. My feeling is that most everything after 1950 should have a signed crown, though I'm not sure about some models, e.g. early S.58's.
I think the signed crowns (Z-in-Star) start with the stellina, the little applied star at 12 o'clock on the dial... so I don't expect earlier watches without applied stars to have signed crowns.
I think the signed crowns (Z-in-Star) start with the stellina, the little applied star at 12 o'clock on the dial... so I don't expect earlier watches without applied stars to have signed crowns.