Instructions
Identify what kind of coin it is. Look for an indications of both its numeration and denomination (i.e., is it 5 pesos? 50 centavos?). These numbers will usually be fairly large on the coin and can be often found on the "tails" side. One important thing to note is the changes in the currency over time. The real and escudo are monetary units from the early 1800's, with 16 reales being equivalent to one escudo. The peso and the centavo were then used from 1863 onward (100 centavos equals 1 peso). In 1992, however, the "new" peso was introduced, with one new peso being equal to 1000 old pesos.
Find its minting date. This number will usually be smaller and found towards the bottom of the coin, and will make it much easier to identify the coin later.
Look for major features of the coin. These features will involve easily noticeable differences in the "heads" side of the coin (often an eagle) and in the tails (which can have many different designs).
Look for smaller details. Both the "heads" and "tails" side may contain markings and etchings that will help you identify the coin. For example, a small letter next to the minting date may indicate what mint the coin is from, as can other minor variations, such as the number of ridges on the edge of the coin.
Look for other distinguishing features, such as a change in the material the coin was made with. The metals might be similar in color (a change from silver to nickel), but can seriously change the worth of the coin. Look for slight changes in hue (after a thorough cleaning) and use a book to help you identify the timing of any metal changes.