What are these silver coins? I tested them with the ice and sound tests, and they appear to be silver.

Alan Chenkin, Novice coin collector and hobbyist

Coin in question:

Based on a quick look, that appears to be a token for a Japanese “Pachislo” skill-stop slot machine. They are usually a stainless steel or aluminum alloy. Pachislo tokens are lightweight and non-magnetic, to prevent any influence on the outcome of the slot machine wager.  The only thing “silver” about them is the color.

Here are some from a google search:

This is a Pachislo skill stop slot machine:
The tokens are “approximately” the size of a US quarter. These tokens are not rare, but specific ones may be hard to locate. They also work in some gaming machines at Chuck E Cheese[1] , and some arcades[2].
I have owned several Pachislo machines, usually reconditioned ones from Japanese cruise ships.  They are usually noisy and have bright lights, which makes them lots of fun, especially when they pay out winnings!  Most machines are easy to maintain, and there are companies devoted to parts and service.  Many owners convert their machines to us US Quarters, although I liked the tokens, and frequently needed to buy more (which is how I learned so much about them).  Reconditioned or used Pachislo machines can be bought for around $500 (USD) – LCD display machines are more expensive, and older machines can sometimes be found on Craigslist or Letgo.  If you buy one on Ebay or Amazon, verify the shipping cost, because they are heavy.  If you have a playroom or home bar, a pachislo machine (or two) can be a fun conversation piece.
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Edited and expanded from my Quora answer.

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