Solid gold trim
Gold filled trim is the norm in vintage pens, but solid gold was also used on occasion. 14K was most often used on American-made pens, and in all cases the gold content marks should be clearly visible. English pens are typically found with 9K or 18K gold trim bands, which will bear hallmarks. In many cases these pens will have clips and levers that are gold filled and not solid gold. Even fully-overlaid 9K English Watermans normally came from the factory with gold filled trim.
Sheaffer is the American brand most likely to be found with solid gold trim, and one also sees a fair number of Watermans from the teens and 20s with 14K barrel bands and sometimes clips and levers as well. Parkers with solid gold trim are quite rare, with the exception of 51s from the 1940s (which are still far from common). Solid gold bands are typically engraved with names, monograms, or other inscriptions; in many cases, the cost of these bands included the cost of engraving.