
Well, thanks to the 21st century and internet research capabilities I quickly discovered this mark belongs to Francis Holmes Boothby! She is a well known and listed Modernist jewelry maker active in the 1950s / 1960s. Her work pulls designs from nature and includes whimsical birds and owls as well as items using a unique convex elliptical form. A quick search of "fhb elliptical" using Images on Google will give you more great peeks at her style.
There is an excellent research article, The Wearable Art Movement Part II , by Marbeth Shon, at Modern Silver.com There is a short piece about Francis Homes Boothby confirming her participation in the 3rd Annual Exhibition of Contemporary Jewelry at the Walker Art Center, Minneapolis in 1955. If you love Modernist jewelry - this is a great article to review!
Although only the earrings are marked in this set, it sure seems that the pin is an unsigned fhb as well. It is actually very small at only 29mm L x 22mm W. The ends have her characteristic "flattened" twist changing the form from circle to ellipical. This wonderful shape is seen in pendant and bracelet designs that she did. But alas there is not one image on the web to make 100% confirmation --so the mystery still continues. Is it a one of a kind? That would be fun.