swamperbob: could you post an image of the other side of the "coin"? Surely you have already done the relative density test, is it silver? Is it cast or struck?
In relation to the date... between 1762-1764 there was a revolt around San Carlos City (Binalatongan) in the Negros Occidental Province in Philippines known as the "Palaris Revolt", its leader was Pantaleon Perez also known as Juan Palaris, due to his skill fencing a rattan or bamboo cane. Palaris was said to possess the power of an anting-anting which made him invincible. The Spaniards eventually defeated Palaris, but at a very high cost, since more than 1200 rebels were killed with a vast destruction of property. Charles III heard of these facts (basically the destruction of the premier city of a province including its main church) and ordered the transfer of the city to another place for a new beginning and a new name for it (San Carlos City). The construction of the new church began in 1770, built with bricks the building is 89 meters long, 22 meters width and a height of 18 meters.
So maybe an amulet invoking the invincibility of Palaris with the date of the new church, but this is a very local event, and the anting-anting as mentioned are widespread in the Philippines, so who knows...