Doesn't really look like an obvious OMM or RPM; I lean towards calling it VAM-14:
http://www.vamworld.com/1890-S+VAM-14
Although there are no pics, the listing describes it as having filled loops in the mint mark. Given a little circulation wear such as your coin shows, I'm thinking that what filled loops would look like.
http://www.vamworld.com/1890-S+VAM-14
Although there are no pics, the listing describes it as having filled loops in the mint mark. Given a little circulation wear such as your coin shows, I'm thinking that what filled loops would look like.



























