The shape puts me in mind of the early Massachusetts Shillings.
The uneven shape in a coin is referred to as a "wavy planchet". A planchet is the blank piece of metal used to strike the impression of the coin into.
In very early coins, planchets were individually cast in moulds or chieseled out of a sheet of metal by hand. In the 1500-1600's, planchet machines were developed to stamp the blanks out of a sheet of metal like a cookie cutter.
Your's certainly appears to be cut by hand.
Reeded edging on coins is a difficult process when it was first developed in the 1700's in Germany and perfected into the 1800's. It involved a machined collar that fit around the planchet so that when the inscription on the coin was struck, the planchet expanded into the collar pressing the reeded into the edge of the coin. These collars were closed, and perfectly round.
However, since the process of reeding a coin was complicated and slowed down coin production considerably, it was traditionally done only on higher value gold and silver coins.
Reeding was done for a couple of reasons, as a deterrant against the common practices of counterfeiting and coin clipping. The effect of the reeded edging was very difficult to simulate by counterfeiters. As well, the reeded edging made it easy to see if the edge of a coin had been "clipped" or shaved down by individuals stealing a little of the metal at a time before passing on the coin.
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In any case, the edge on your piece looks as if it was filed by hand to look like reeding, and certainly not a result of being stamped in a round reeding collar during coin production. It appears to be the work of an individual, perhaps a crude blacksmith token or a decorative "love" token.
One other thought... it could be a real worn Spanish Maravedis coin. These were copper and produced in the 1500's (see below) In the 1600's many of these were counterstamped with a date (1655 is common) and roman numerals (XII) to double their value. Some of these are worn so badly that all you can see are the counterstamps. Same kinda shape as yours. Could be that because of the wear, the coin was no longer accepted, and someone tried the reeding trick to make it look like a coin again.
http://www.vcoins.com/ancient/davidconnors/store/listCategoriesAndProducts.asp?idCategory=44
Seems like a lot of effort for a blank piece. Have you tried smearing a little olive oil on the surface to see if it will bring up any faint designs or inscriptions when you hold it to the light?
Interesting find, thanks for posting!
--Steve