On my random internet walk this evening, I ran across the following symbols. I’m sure they have no relation to the Halloween card, but they did briefly pique my interest, so I’ll add them to the the noise.

The alchemical symbol for Nitric Acid (Aqua Fortis):

The 5 eyes on the left bottom inside of the card reminded me of the constellation Crux:

Crux is also known as the Southern Cross. It’s depicted on the flags of Australia and New Zealand.

So putting it all together, Z was telling us that he was an Ozzie/Kiwi Chemist/Sailor/Astronomer.