I don't think the signature devalues the vase, for some it might even hold extra interest. I thought of starting a fake signature collection when I had two wonky signatures on genuine bits of Mdina. Eventually I auctioned them on ebay and they did fine (pointing out the dodgy sigs), one was spelt wrong, in capital letters and in the 'wrong' place, quite comical really.
Again, lovely bit of glass, I'm quite :mrgreen:.
John