I think the number 10/12 signifies this is number 10 of a series of 12 "Lovers" sculptures. I found another page with different figures numbered 1/12 and 8/12 etc. I don't think it is the number cast, as all 3 photos I have found of 10/12 have slight differences, eg grain on the wood on the bases, some degree of oxidation of the bronze etc. I think this one is number 10 in a series of 12.

http://www.aasd.com.au/subscribers/list_all_works.cfm?concat=TribeRhond&start=21&show=10