X, etc.
My own feeling about the X shape in the Wands pips is that it is the Greek letter "chi", the "CH" sound that begins Christ's name. The letter "r", known in Greek as "rho", is written in Greek like our capital P, which looks like the upright wands on the odd numbered pips. This "chi-rho" shape, as it is called, is the symbol on the Catholic tabernacle (is it?), which is the box that holds objects used during the Mass.
If you put the cards of the Swords suit side by side the curved swords make a series of completed circles and as the suit progresses resemble the round labyrinth designs on the floors of cathedrals.
Cups bring to mind the eucharist and the receptacles containing Christ's blood.
Coins reproduce the shape of the bread, or host, the body of Christ, also used during the eucharist.
The Marseille tarot was created for a Catholic Christian culture so I think these shapes would have been instantly recognisable to its audience. Christian symbolism permeated every aspect of their lives, even a deck of playing cards. Four suits = four Gospels, etc.