1. No Mint Mark: Coins produced at the Philadelphia Mint do not have a mint mark. Therefore, if there is no mint mark below the date, the coin was minted in Philadelphia.
2. "D" Mint Mark: Coins produced at the Denver Mint have the letter "D" as the mint mark. The "D" mint mark is located on the reverse (tails side) of the coin, directly below the eagle emblem.
So, depending on the presence or absence of the mint mark, you can determine whether a 1776-1976 Eisenhower silver dollar was produced in Philadelphia or Denver.