Firstly, I noticed the mathematical sequence into which these signs fit. Beginning at Aries, one counts two signs before Gemini, the third sign. Then, one counts three signs before Libra, the seventh sign. To end, one counts four signs before Pisces, the twelfth and final sign. The space between each pair sign grows as one proceeds around the Zodiac: two, then three, then four. What immediately comes to my mind is the potentially spiraling effect this could imply. The pair signs are therefore very important, signifying a spiraling outward, growth of consciousness, transcendence.
Second, I thought of the widespread importance of the numbers three, seven, and twelve. Gemini, Libra, and Pisces occupy these positions in the Zodiac. Many are the cultures who have highlighted three, seven, and twelve as spiritually significant numbers.
Overall, I think recognizing these pair signs plays into defining the human being as a social creature. Seeing that there are no pair signs at the very bottom of the Zodiac, one is reminded that in death one dies alone. But this discussion need not be entirely grim; the bottom of the Zodiac is also associated with introversion and the subconscious, as well as philosophy and abstract, independent thought. To cut this discussion shamefully short, one may do well to pay attention to the properties of these pair signs and how they inform the sociology of sacred mathematics and a deeper understanding of the human psyche.