There are no reports of 1977-D quarters struck* on silver planchets**.
Two things to check:
First, look at the coin's edge. If it shows any copper, you have an ordinary quarter.
Second, if the edge is the same color as the face, compare the coin's weight to an ordinary clad quarter. A silver quarter will be substantially heavier (6.25 gm vs. 5.67 gm). Use a Popsicle stick balance if you don't have an accurate scale.
If the coin weighs the same as a normal quarter, it's simply been plated for use in jewelry or similar.
To clear up terminology:
(*) Coins are struck or minted, not "stamped".
(**) They are struck on blanks or planchets, not "plugs".
No US quarters are dated 1975, all have the dual date 1776-1976
It's just a state quarter that has been gold plated and it has no collectible value at all, unless you find someone that wants it.
It depends on how far off center it's struck, take it to a dealer or collector for a better idea of value.
The word COPY should be a very large clue telling you that it's, uh, well, um, a copy.
Assuming your silver proof quarter does not have any visible nicks or scratches, it is worth $3-$4 -- otherwise it's worth about $1 (Deleted my previous update. Since the S mint mark only appears on proof coins this could not be a circulation strike. The first answer above is correct as it stands.)
No US quarters are dated 1975, all have the dual date 1776-1976
Do you mean a quarter DOLLAR? Quarter eagles were not issued in 1968. And could you describe "double 'stamped"" ? (note the term is actually "struck" in coin jargon).
This is a rare misstruck error and is worth up to $90.00 according to condition.
37,600,000 Thirty seven million, six hundred thousand Northern Marina Islands Quarters have been stamped and let out for the public banks. There will not be any more of these quarters produced because this certain quarter represented the sixth and final release of the 2009 DC and US territories quarter program.
There is no one particular state that is double stamped -- it could happen to any of them.
1¢
The production year is not stamped on a gun. It is the serial number that is used to tell which batch was made in a particular year. Go to: proofhouse.com for listings.
25 cents
25 cents
The 'Eagle Reverse" was last used in 1998 for the Washington quarters. Look at the reeding on the edge of the coin. You should see a seam an the reeds won't mach up. This is NOT a U.S. mint error coin. It has been altered and has no numismatic collectible value.
This type of quarter was designed by Hermon A. MacNeil. The M is MacNeil's initial.
August 1, 2009 The US Mint has not issued a quarter with an "M" stamped on it. Probably what you have is a quarter that someone has put their initial on or marked it for some reason. With such a mark it has no numismatic value but is worth $2.52 for the silver it contains.