That, young lady is one of my favorite coins! An American Standing Liberty Quarter dollar. As there is no discernable date is is sold as scrap. Coin Highlights:
- Contains .17875 oz of Silver.
- Designed by Hermon MacNeil.
- Obverse: Depicts a militaristic Liberty wearing chainmail walking through a gate while holding an olive branch and a shield.
- Reverse: Depicts an eagle in flight.
I agree with John. One of my favorites, too!
Miss Liberty is standing. There was a scandal when the coin first appeared. The original 1916 coins showed Miss Liberty bare breasted. The mint covered her up soon thereafter.
Containing about 0.18 troy ounces of silver, with silver currently trading at about $20 per troy ounce, your coin is worth about 0.18 x 20 = $3.60.
You can see a complete write-up on Standing Liberty Quarters at this page:
Personal counterstamps happen all the time. Some collectors seek them out. Most consider them post-mint damage. I don't think it affects your coin one way or the other. See this page for more info: