Silver Dollar.

[Bump73]

I found this coin and was trying to figure out what this mark by the eagles beak and wing.

 

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[l.cutler]

It appears someone may have been trying out a letter or number punch.

 

[ARC]

I have seen a few of these over the years.
I have seen a peace dollar with this... a buffalo nickel and at least one other coin with this stamp.

So its not just yours that has this... and the mark is either an O or a zero... unsure on this... but the ones i have seen are identical.

 

[pepperj]

The full pictures shows it off better.
I'll still go with a counter stamped-reasons unknown
Really a nice silver.

 

[tamrock]

Possibly a type of chop that indicates the weight of this worn down silver dollar has be validated by some merchant. ?