In Latin America, the devout often petition a saint for a favor or thank him for answering a prayer by hanging a small representation of the petition on his/her image. These devotional miniatures, generally made of silver or silvery-colored metal today, are called milagros (miracles), or milagritos (little miracles). In some cases, people refer to these tiny effigies--of a person, a house, an animal, crop or vehicle, etc.--as ex-votos, Latin for "from a vow." Oftentimes, a person makes a vow or promise (a promesa or a manda) to the saint to give her a little present when she answers the petitioner's prayer. The quantity of milagros on a saint testifies to the saint's effectiveness in answering prayers.
Customs such as the use of milagros are ancient, timeless, and nearly universal. In the Latin Catholic world, the milagro of a baby asks for a safe pregnancy and birth; the image of a soldier prays for his safe return; a heart may symbolize a love affair or cardiological problem. Basically, the petitioner decides what a milagro represents.
There are no fixed rules about what a specific milagro represents.
Today, many people use milagros to wish a friend well with a serious disease or a concern: a horse miniature for a child hoping for a pony, a car milagro to wish a friend a safe journey or a trouble-free car; a foot milagro for a jogger; a house milagro to wish someone luck in obtaining a mortgage.
--See Martha Egan, Milagros - Votive Offerings from the Americas (Museum of NM Press, 1991).