This is he Greek philosophical symbol, Phi. The left one is the uppercase whereas the right one is the lowercase. Just like the ying yang symbol, it is a representation of balance. This symbol denotes the golden ratio, which is a mathematical and arts thing where “the sum of the quantities to the larger quantity is equal to the ratio of larger quantity to the smaller one.” (Wikipedia). Artists and architects of the Renaissance period would perfect their work to the golden ratio as symmetry is pleasing to the eye.