What do the roman numerals on this piece of jewellery mean?

I have never been into jewellery much, but my boyfriend buys me stuff all the time. He always buys white gold, usually from Tiffany's, and has great taste, but yesterday he gave me this necklace with a pendant that I don't understand. I found a link for a replica version of it. The chain is different but... show more I have never been into jewellery much, but my boyfriend buys me stuff all the time. He always buys white gold, usually from Tiffany's, and has great taste, but yesterday he gave me this necklace with a pendant that I don't understand. I found a link for a replica version of it. The chain is different but the pendant is exactly the same. I thought maybe you are suposed to customize the numbers... I don't know. Anyone else have any ideas? You can click on the link to see what it looks like but the numbers are 3, 6, 12

Thanks!
Update: I'm an idiot, sorry. Here's the link:

http://www.evesaddiction.com/detail_NLZ10105__218__Tiffany_Inspired_Cubic_Zirconia_Atlas_Bar_Pendant.html
5 answers 5