... if I saw this offered for sale my doubts are strong enough that I would pass it by.
That is perfectly understandable; still I guess you would have probably bought it if you found it in a charity shop for 6 Euros

I see no difference in the tool used, comparing the mark on the Ann Wärff bowl I linked to above, with mine. Most of the other pieces I found on the net are marked with a different tool, I agree. But still very inconsistent.
And I am really not expecting a "fake" Mona Morales piece to turn up in a charity shop in Austria.
The shape and the base finish would perhaps lead me towards Kosta even if it was unsigned. (Not to this designer, I admit

)
Apparently she stopped using Schildt after her divorce in 1964.
I thought the same -- not using the name "Schildt" in the mark might point towards production between 1964 and 1971 (assuming that we have a genuine piece here).
Thanks,
Michael