I wondered if they might be an Alchemy Symbol....is there an Alchemist in the house? Might it have been made for a chemical industry giveaway?
I can see what you mean Nancy, there are 2 that are different, but I have to confess I would never have spotted that myself!!
I'm beginning suspect you might be correct Peter....a learners piece?
On the other hand, I know nothing about paperweights....I only have 2 to my name!