U.S. coins have never carried an R mint mark. If you have an American coin with what looks like an R on it it could be either damage or possibly the monogram of the coin's designer. Please post a new question with enough details to identify the specific coin in question.
No mint mark indicates that the coin was minted in Philadelphia.
made in the Philadelphia Mint
The letter is known as the mint-mark and tells where the coin was made. A coin having a P mint-mark (or no mint-mark on some coins) was made in Philadelphia, a coin having an S Mint-mark was minted in San Fransisco, a coin with a D mint-mark was minted in Denver.
The mint mark on all Washington quarters dated from 1932 to 1964 is on the back side above the "R" in the word Quarter. No mint mark = Philadelphia S = San Francisco D = DenverOther datesQuarters dated 1965-67 don't have mint marks. Starting in 1968 the mint mark was moved to the right of the tail of Washington's wig, and in 1980 Philadelphia coins started using a P mint mark.
JS isn't the mint mark, but rather the initials of John R. Sinnock, Chief Engraver of the U.S. Mint. A 1950s dime will have a D for Denver, S for San Francisco, or no mint mark for Philadelphia (a P mark wasn't added until the 1980s). 1956 is a common date, currently worth about $2 for the silver.
There's no "R" mint mark. The mint mark position on a Seated Liberty half should be below the eagle. If the "R" is elsewhere your coin has been altered and has lost most of its collector value. If the R is where the mint mark should be please check it with a good magnifying glass. There's more information at the Related Question.
No mint mark indicates that the coin was minted in Philadelphia.
made in the Philadelphia Mint
US Coins with no mint mark were minted at the US Mint's main facility in Philadelphia, Pennsylvania.
The lack of a mint mark usually indicates that the coin was minted in Philadelphia.
Sorry that was suppose to say a mint mark of an "A" on the PFENNIG.
The letter is known as the mint-mark and tells where the coin was made. A coin having a P mint-mark (or no mint-mark on some coins) was made in Philadelphia, a coin having an S Mint-mark was minted in San Fransisco, a coin with a D mint-mark was minted in Denver.
On an US coin it can mean "cents" or it can be the mint mark of the Charlotte Mint, which existed only from 1838 to 1861.
The mint mark on all Washington quarters dated from 1932 to 1964 is on the back side above the "R" in the word Quarter. No mint mark = Philadelphia S = San Francisco D = DenverOther datesQuarters dated 1965-67 don't have mint marks. Starting in 1968 the mint mark was moved to the right of the tail of Washington's wig, and in 1980 Philadelphia coins started using a P mint mark.
I'm assuming you mean the mint-mark? The mint-mark shows which branch of the US mint created the coins, if there is a P mark (or no mintmark on some coins) the coin was minted in Philadelphia, a D mark signifies Denver, an S mark shows the coin was from San Fransisco and a W mark is from the West Point Mint.
Cents struck at the Philadelphia mint don't have a mint mark.
If you mean a Buffalo Nickel with no mint mark, it was struck in Philadelphia. The P mint mark was used on nickels for the first time in 1980