Many people collect coins. Linked below is a list of 5 of the most valuable Tsarist era Russian coins that went to auction. These are incredible.
https://www.rbth.com/lifestyle/330191-most-valuable-coins-tsarist-russia
Coin collectors, or Numismatists, are a patient bunch. I’ve seen them at flea markets sit in the same spot for hours just paging through the coins that are for sale. Looking for that one coin that they need to add to their collection.
If you think you have a valuable coin: Do Not Clean It! Cleaning a coin even with soap and water can cause micro-abrasions that can change the color and shine of the coin, which in turn will lower the overall value of the coin.
Also: Don’t touch the face of a coin. Hold it by the edges, get cotton gloves, or use coin tongs.
Source: http://www.silvercoins.com/coin-collecting-guide/#grading
Here are some tips regarding US coins:
For US Coins there is usually a small letter on the front, also called the Obverse side, or back, called the Reverse side, which indicates at which US Mint facility the coin was minted. Prior to 1965 you’ll find it on the reverse of the coin, except for the cent coin, which has it on the front. After 1967 the Mint Mark is on the obverse.
Coins without a Mint Mark were probably struck at the Philadelphia Mint prior to 1979. Philadelphia was the only location that minted coins originally. So there was no need to identify where they came from.
Source: https://americanfederal.com/coins/us-mint-marks/
For a list of all the US Mint locations see the American Federal website linked above.
Coins minted in 1965, 1966, and 1967 have no mint mark. Read about why at:
https://www.usmint.gov/learn/collecting-basics/mint-marks
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