Vintage Rhinestone Circular Wreath Brooch

Pretty sparkly piece with minor discoloration of a couple of the rhinestones that are not totally white. Very tasteful filigree pattern with center portion being more raised than the outer portion. I've tried to magnify this a lot to try to make out what it says on the back, but nothing is clear enough. There's definitely some numbers and letters. I've searched all over the Internet and I found a couple of sources - but it's still not identifiable.