Hello!
I have not visited this site for a long time and not noticed this question.
Raakel is right. I did get the knowledge afterwards and mailed it to Bob.
There has been a period when US authorities demanded the initials of the engraver on imported birds, just like Raakel wrote. I do not know the reason or the time for how long it lasted but it is dated at the time of the Birds of Passage. Whether the way of importing/exporting is essential I do not know.
There may also exist other initials than IT. BTW Inkeri Toikka engraved quite a lot of signatures on birds and other art glass in Nuutajarvi, I mean in a "normal way".
Happy springtime to all Toikka bird-lovers!