1927 P Standing Liberty Quarter - Circulated

Worn, Portsmouth.

Likely "P". Star at bottom where mint mark is barely visible. However, it is visible. The device adjacent is flat, it appears there was no mint mark there.

In short, my guess it being "P" is based on the star not being completely worn off and the space with the mint mark (if not "P", is not worn away). Thus, there never was a mint mark there, if there was, it would still be visibile to some degree since the star also is.