It can only be on the front, back or edge of a coin.
The mint mark is located on the reverse [tails] side of the coin at the bottom below the wreath. If there is no mint mark then the coin was minted at the Philadelphia Mint.
It depends on the type of coin the date and denomination on were the mint mark is located
If it doesn't have a mint mark, that means it was made in Philadelphia.
The lack of a mint mark usually indicates that the coin was minted in Philadelphia.
The mint mark on any Morgan dollar is on the reverse above the letters DO in dollar.
A mint mark tells where the coin was minted, for example, a P mint mark (or in some cases no mint mark) signifies the coin was minted in Philadelphia, D is for Denver, S is for San Fransisco. I'm assuming someone told you that the mint mark was under the eagle for whatever coin you had, so you simply need to look under the eagle to find a mint mark. Keep in mind that some coins were produced in the Philadelphia mint and have no mint mark.
You look at the mint mark. If it is a D, then it is Denver, if it is a S, then it is San Fransisco, if it is a P, it is a Philadelphia.US Coins carry a mark to identify the mint.
The mint mark on Eisenhower dollars is on the front, below Ike's neck and above the 7 in the date.
Usually on the reverse, at the bottom between the eagle and the rim.
On Morgan dollars (the type minted at the time), the mint mark is on the back, towards the bottom, just above the letters "do" in the word "dollar." And if there's no mint mark, it means it was minted in Philadelphia.
On the front below " In God We Trust".
Normally you have to know a coin's denomination to locate the mint mark because it can be in different places. Also, Philadelphia did not use a mint mark on most coins until 1980 so it's very possible your coin doesn't have a mint mark. Once you know the denomination you can check a site such as www.coinfacts.com that shows the mint mark locations for all US coins.