Advice on how to research RD (registered design) numbers.

Can anyone please give this newbie some advice on how or where to research registered design numbers.
These vases were sold by a gift shop in Chatswood Australia around the 1950's. (I think).
The one on the right is from the same lot and looks to be from the same maker, similar color, texture and style etc, but has no marks.
The one on the left has a signature which I don't recognize and RD58283, or 59283, marked on bottom.
Both stand around 20cm tall (8 inches).
Any help with either the number or the signature is greatly appreciated.
(or how to clean it :-) )

If it was a British registered design number it would be for 1886 and the vases do not look to be from that period. Therefore it is more likely to be an Australian one so your local reference library might be your best bet.

Greetings and thanks for the reply.
It inspired me to look harder and I found the website for the Aus.gov design data base.
http://www.ipaustralia.gov.au/get-the-right-ip/designs/search-for-a-design/

Unfortunately online records only go back to 1985 so looks like I will have to make a trip into the nearest office and look through the records. (Or pay $50 and they will do the search and send me a copy via email).
Thanks again.

It would probably me something similar here and a cost involved so that's why I suggested a local reference library. There you might find out the date of registration and then decide if you wish to take it further.

Just updating this with recently found information on the mark to help out anyone who may search for it in the future.
Mark is Rathjen.
Henning Rathjen (1903-1968), whose pottery was often glazed in pastel pink or an off-white glaze sprayed on to achieve a highly textured dry surface. Rathjen studied pottery at both the Caulfield and Royal Melbourne Institute's of Technology. He set up a pottery studio in 1947, producing a variety of slip cast wares until the late 1960s. Examples of his work exist in significant public collections such as Shepparton Art Gallery's permanent ceramic collection and the Ballarat Fine Art Gallery Collection.