This paperweight is signed OM and made by the noted Australian glass artist Setsuko Ogishi at her Ogishi-Mizuno studio at Rothbury in the Hunter Valley north of Sydney. See the two examples below of the signature and a sticker from the studio. She has an extensive website here
There is a similar apple paperweight on the website of an Australian collector here
. It doesn't show the signature, but that collector lives in the Hunter Valley and knows his Ogishi (and other) glass.
I note that this solution is 5 years and 80 days after the original query was posted. That is a new personal best for me, up from my previous record of 4 years and 354 days, seen here
I hadn't looked before for stray Australian studio glass in the Paperweights section of the GMB. Who knows what else I may find?