About Mexican crosses (from the web):
The Mexican cross has become an integral part of Mexican folk art. It is seen everywhere in Mexico -- on home altars, in roadside shrines, worn by the faithful. Mexican crosses are found molded from clay, hand-carved from wood and brightly painted, covered with milagros, in the form of tin and glass nichos, cast in silver and pewter, and in almost every medium imaginable! Milagros are religious folk charms that are traditionally used for healing purposes and as votive offerings in Mexico. There are many fine craftspersons in clay, so there are many fine clay crosses. Carved and painted wooden crosses are covered with many different motifs.
Here are some some Milagros; the word means "miracles" in Spanish. Milagros of a body part such as a leg might be used as part of a prayer or vow for the improvement for some condition associated with a leg - such as arthritis. Or, it might refer to a concept such a travel, the leg implying walking. Similarly, a heart might represent a heart condition that one is praying for a cure or more often as a thank you for answering the prayers of the lovelorn.