All 1988 quarters should have a mint mark next to the tail of Washington's wig - P for Philadelphia, D for Denver; or S for San Francisco on proof coins.
If there isn't a mint mark you could have a filled-die error where some crud got into the little recess in the die that forms the D or P, or someone could have altered the coin. Use a strong magnifier to see if there's evidence of a mint mark next to the wig. If it looks absolutely flat, no evidence of alteration, your best bet would be to have it examined in person by a professional dealer or appraiser who specializes in error coins. They'd have the high-quality equipment needed to make a better evaluation.
How much
This date regardless of mint mark is valued for the silver and is worth about $3.25
It is worth $1 in mint condition.
No mint mark means it was minted in Philadelphia. The quarter is worth exactly 25 cents.
It is worth .25¢ The absence of a mint mark simply means it was minted at Philadelphia.
No U.S. coins dated 1966 have a mint mark. The '66 quarter is worth 25 cents.
how much is a canadian mint quarter worth
All U.S. quarters since 1980 have mint marks. Being that it's still 2014, even a mint condition 2014 quarter is worth 25 cents.
This date regardless of mint mark is valued for the silver and is worth about $3.25
A mint condition 2008 Arizona quarter is worth an estimated 95 cents.
It is worth $1 in mint condition.
It's worth 25 cents.
No mint mark means it was minted in Philadelphia. The quarter is worth exactly 25 cents.
25 cents.
It is worth .25¢ The absence of a mint mark simply means it was minted at Philadelphia.
A 1934 Washington Quarter in good condition (G4) is worth: $3.50. If its mint state is MS60, the value rises to: $$45.
25 cents
It is worth face value unless it is still in the original mint package.