Hello and welcome to the Board.
As you suspect, what you have there started life as something else - in this case a perfume bottle, now missing its stopper. The maker is Micheal Hook, an Australian artist who trained at the Jam Factory in Adelaide 1979-82 before working at Nick Mount's Budgeree Glass in Victoria and then setting up his own studio called Resolution Glass in inner-suburban Melbourne. I think he has recently closed the studio and retired from glass making.
I don't have a bottle in exactly the same design as yours, but the photos below show the general shape of yours and another bottle with some similar characteristics and which could well be turned upside down after removing the stopper.
It was rather creative of your vendor to invert it and call it a 'paperweight'. Usually they advertise a small bottle that's lost its stopper as a 'posy vase'. Here is one such example currently on ebay.au
http://www.ebay.com.au/itm/MICHAEL-HOOK-ART-GLASS-BUD-VASE-PERFUME-BOTTLE-CONTROLLED-BUBBLE-SIGNED-/271556340453Michael Hook did make paperweights in the same general design as your bottle. There are signed on the bottom in the regular way, as you would expect.
If I google for "Michael Hook glass" and then switch to 'images', I get lots of pictures of his bottles and paperweights. That may be because I'm getting the feed from Google Australia, but it may be worth your while to try it.
Thanks for a wonderful query.
Trevor