The only nickels* struck at San Francisco since the 1970s have been proof coins. Someone almost certainly broke open the case that held the original proof set and spent its contents. Not terribly bright, because a proof set costs much more than face value.
Unfortunately a proof coin that has been circulated loses its value due to damage from other coins, exposure to air, etc.
(*) To clear things up, the coin is called a nickel rather than "nickle"
If your coin has a "S" mint mark on it means that it was made at the San Francisco mint in California.
On a 1962 nickel, the mint mark is located on the reverse side of the coin, to the right of the building depicted in the center. It can either be a "D" for Denver or an "S" for San Francisco, depending on where the coin was minted. If there is no mint mark, it was minted in Philadelphia.
You're probably seeing FS, the initials of the coin's designer Felix Schlag. All 1988 nickels would have either a P, D, or S mint mark. Any that you find in change are worth only face value. The last time the US used a double mint mark was 1893, on coins struck in Carson City.
The value would depend on the condition and date of the coin.
On the back, to the right of the base of the building. No mint mark = Philadelphia D = Denver S = San Francisco
If the mint mark is a D the nickel is probably worth no more than a dollar. If the mint mark is an S it could be worth around $3.00 By the way, there is no such thing as a 1938 liberty nickel. The only nickels minted in 1938 were buffaloes and Jeffersons.
1976, Kennedy Bicentennial Half Dollar; with no mint mark, copper-nickel clad, uncirculated-$1.25 with D mint mark, copper-nickel clad, uncirculated-$1.25 with S mint mark, copper-nickel clad, proof-$1.75 with S mint mark, silver clad, uncirculated-$4.00, proof-$5.00There were so many hundreds of millions of these minted that if your coin has been in circulation, it has no added value and probably never will.
It would depend on the date of the Buffalo nickel. Post a new question and include the date and mintmark if there is one.
1976, Kennedy Bicentennial Half Dollar; with no mint mark, copper-nickel clad, uncirculated-$1.25 with D mint mark, copper-nickel clad, uncirculated-$1.25 with S mint mark, copper-nickel clad, proof-$1.75 with S mint mark, silver clad, uncirculated-$4.00, proof-$5.00There were so many hundreds of millions of these minted that if your coin has been in circulation, it has no added value and probably never will.
1976, Kennedy Bicentennial Half Dollar; with no mint mark, copper-nickel clad, uncirculated-$1.25 with D mint mark, copper-nickel clad, uncirculated-$1.25 with S mint mark, copper-nickel clad, proof-$1.75 with S mint mark, silver clad, uncirculated-$4.00, proof-$5.00There were so many hundreds of millions of these minted that if your coin has been in circulation, it has no added value and probably never will.
It's a mintmark indicating the coin was minted in San Francisco. Possible letters on a buffalo nickel are:No mint mark = PhiladelphiaD = DenverS = San Francisco
If it has one, it's on the reverse under the words FIVE CENTS and can only be an "S"