Within these squares are the letters :

P / 8/ E

PL / SVL / TRA

E / 58 / P

In the mid-16th century major silver deposits were found in South America, in an area known as 'Peru', but this relates to an area much larger than modern-day Peru. Coins minted from here were called 'cobs' or cabo, and rather than producing a nice flan onto which the image was struck, cobs were simply a bar of silver cut into appropriate weights (1, 2, 4, 8 reales) so they are not standard shapes.

Cayon (2005) illustrates a similar eight reales minted in Potosi and dated to 1658 on page 711, fig.111, no.6503.