It started with a small observation while watching the anime. But after reviewing a few images from the light novels as well, I am now convinced that each of Touya's nine brides have astronomical symbols deliberately added to their clothing;

Linze's Brooch looks like the symbol for Neptune (♆)

Else's could be argued to look like Venus (♀)

Leen's looks like Mercury (☿)

Lucia's looks like Mars (♂)

Yae had the Moon printed on her kimono (☽︎)

Sushie's bracelets and necklace have Uranus (⛢)

Yumina's hair is held by what could look like the Earth (?)

Hildegard's coat beneath her armour have Jupiter (♃)

and Sakura's pendant has the Sun on it (☉)