I too don't remember fountain pen nibs held on such a gadget. They were more commonly packaged in a small box. But perhaps if a writer had several nibs of different sizes (as a calligraphy artist might use), there would have been some need for the Shrimp Spearer in such capacity. It could also have been used to mark onto carbon paper, that is, to write a sort of "secret message" on the copy-sheets without making an ink mark on the top-most, original sheet. Aside from 007 types, I don't know why one would put the device to such a use.

By the way, if any of you have old fountain-pen nibs, be sure to send 'em my way. The golden-colored ones were often 14k but the darker silvery ones were sometimes made . . . of rhodium.