What is unique or rare about the VM Zodiac signs?

[Koen G]

The drawing style, dress, faces and even the trees in the background all look period appropriate. So even if they were not original, then I'd say the design certainly is. 

If this is a man and a woman, then the pose is what I'd expect of a marriage or betrothal contract, whereby they hold hands while the man offers an object to the woman.