"This prayer dates to an incident in July 1729 in Spain. A merchant's wife, in need of support from her husband on business in Peru placed a letter to him in the sleeve of St. Anthony's statue in her parish church, trusting he would somehow deliver it.
Returning to the statue the next day, she found not her own letter but one from her husband, Don Antonio. Lodger in the sleeve was a heavy pouch containing 300 pesos, also sent by him. The merchant advised his wife that a letter from her had been delivered "by a friar of the Order of St. Francis." Don Antonio was sending his reply through the same friar. To this day, the merchant's letter is preserved in the church at Oviedo.
Interestingly enough, I now put the "SAG" on all my bills and important mailings. ;-)
Ecce Crucem Domini,
Fugite, partes adversae,
Vicit Leo de Tribu Juda,
Radix David, alleluia!