A dove is considered a symbol of peace and love. They are often used in various religious traditions including Christianity, Paganism and Judaism.
Although doves vary in color, they are often depicted as being white, typically because of the association between the color white and purity. Doves and pigeons, in general, are the same thing. The word "dove" usually refers to a smaller species of pigeon, and what most people call pigeons are a type of bird labeled a feral rock pigeon.
The idea of pigeons as annoying and dirty is a complete contrast to the symbolism of the dove. Doves are depicted as being messengers of peace and love. This symbolism is present in religious texts including the Bible. In the Muslim religion, it was a dove who spoke God's word to Muhammad.