Portrait Painting Signed with monogram Eagle / Bird inside a circle GERMAN?

I have what I think is a well executed antique portrait of a young girl which instead of a signature has a monogram of what looks like a bird or perhaps an eagle inside a circle - it is painted rather than stamped so I do think this is the mark of the artist.  I don't know much about the history of this but it could originally have come from Germany?  Any help or advice in trying to trace this artist would be appreciated.