Thanks for that information Paperweights.
This weight may or may not have an etched Swarovski logo on the bottom but, as you can see in the pictures, it's covered with black felt! I'll have another good look at it with a magnifying glass tomorrow (in daylight) to see if I can something by looking down at the base through the side. While I agree that most Swarovski pieces are etch marked, I can say from experience that not all of them are ~ I've sold a couple of boxed weights in the past which didn't appear to have any mark (although, given that Swarovski say "it may only be faintly visible or almost impossible to detect", it's possible that I missed it!).
Many thanks again for your help.