That phrase is found on many U.S. coins, so there is not enough information in your question to give a specific answer. That said, on the majority of U.S. coins, the mint mark is on the reverse side if it's dated 1964 or earlier, and on the obverse side 1968 and after.
If the coin does have a mintmark it would be under the "DO" in dollar on the back of the coin.
If you refer to the British Five Pound (Crown) coin, they do not have a mintmark. They were all minted at the Royal Mint in Wales.
If the coin has a Mintmark it is on the back of the coin, above the letters DO in dollar.
Any mintmark will be found on the reverse of the coin under the wreath above the space between the D and O in "DOLLAR". Keep in mind that your coin could have no mintmark, in which case it would be minted in Philadelphia. If your coin has a mintmark, it will ether be a "CC", a "S" or an "O".
If it is a "s" quarter it will always have the S mintmark. You can find this mintmark usually on the back of the coin. The exact location will depend on the type of quarter.
Except on the 1964 issues where the mintmark was located on the reverse of the coin under the olive branch that the eagle is clutching. The mintmark is located on the front of the coin, below Kennedy's face and above the the space after the first 2 numbers of the year. Keep in mind that your coin may have no mintmark, in which case it was struck at the Philadelphia Mint.
The motto E Pluribus Unum is on ALL U.S. coins so that doesn't help with specific identification. Please post a new question with the coin's denomination. Also see if you can find a small mint mark letter such as O or S.
The letter "D" under the date of a penny is the mintmark which indicates where the coin was minted. There are 4 operating mints in the USA. One , represented by the mintmark "D" is in Denver, Colorado. Another, represented by the mintmark "S" is in San Francisco, California. Another, represented by the mintmark "W" is in West Point, New York. The 4th, represented by the mintmark "P" is in Philadelphia, Pennsylvania. You will find these mintmarks on all coins struck in the USA today with the exception of the pennies which are produced at the Philadelphia mint. You will find no pennies with a mintmark "P". You will also find no coin minted in 1965, 1966 and 1967 with a mintmark. This is because during those years, to discourage coin collecting which some blamed for a coin shortage, none of the mint facilities in the US placed mintmarks on the coins they produced. This practice ended in 1967 and in 1968 mintmarks were again placed on US coins.
If your (walking liberty half dollar) coin is dated 1916 (and some 1917 coins) the mintmark is found underneath "In God we Trust" on the front of the coin. All other years the mintmark is found on the reverse of the coin to the left of the branch that the eagle is sitting on. Keep in mind that if your coin has no mintmark, it was minted in Philadelphia. If you have a silver eagle dollar which also uses the walking liberty design, the mintmark will be on the back under the olive branch that the eagle is holding. Bullion silver eagles do not contain mintmarks and could be minted from a number of different mints depending on the year the coin was issued.
Not all U.S. coins have mintmarks. Coins without one were struck in Philadelphia
If it was minted in 2009 and later, the date and mint mark along with the phrase " E Pluribus Unum " are on the rim and not on the obverse or reverse of the coin.
The S mintmark means it was made at the San Francisco Mint. It could be a copper-nickel proof or a 40% silver coin. Both have the same mintmark. Take it to a coin dealer or collector to find out which one it is.