The style of the mark over two lines reminds me of the 'Venini Murano' acid stamp mark. I can't tell from the pics if this mark is engraved or an acid stamp though.
Oh, yes, there's a match!!! That is why it looks like zig-zag !

Thank you!
Like I said, even the finest powder doesn't hang on, so I go with the acid stamp mark.
I would love to find something similar from them. I'll keep oon googling.