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?
Trevor