The upside down M on the Ace of Cups is a mystery to most people, who usually look to the religious mythology, but what if that M is a W? As in the constellation of Cassiopeia. It’s a female image upside down in the northern hemisphere sky. That makes a lot of sense when one delves into the esoteric mysteries the RWS Deck are infused with deep symbolism.
There are 5 stars in the constellation of Cassiopeia that form a W or from the Southern Hemisphere it is an M. In mythology she is the queen Cassiopeia and the mother of Andromeda
A blurb on the myth of Queen Cassiopeia and Andromeda.
The Dove in the card can also represent a constellation called Columba not just the allegorical dove in biblical stories each image within a card is a symbol. There is much more to the images and mythology that is incorporated into the Tarot deck. Apart from the conventional Christian, Greek Mythology, the Tarot is infused with Astrology, Greek, Roman, ancient Egyptian, Mesopotamian and Persian mythology, Numerology, The Kabbalah, Ancient history and Astronomy. Then there is the language of colour symbolism. There are multiple layers of wisdom that are only imparted to certain metaphysicians that is carefully guarded and
https://en.wikipedia.org/wiki/Columba_(constellation)
I do feel there is a strong case for this being a hidden meaning that most Tarot readers have perhaps overlooked. My rule of thumb is always check the skies with myths and if I can't find anything that sounds right then I hold off. But the more I think, and rummage around online I find other things that make me think, oh wait; I need to make notes on such and such. We never stop learning when we step into the realms of the esoteric and metaphysics any you can never know enough no matter how long you have been a reader.