This is an original Edison GEM bulb. In the very beginning of their existence (in 1905), GEM light bulbs had twin hairpin filaments in series (like on this bulb). They were later changed to a single continuous filament in 1909, meaning that this bulb is at least 110 years old, and could be up to 114 years old (as of 2019). The GEM bulb used a filament that was 25-30% more efficient than the carbon filaments used in earlier bulbs (they gave more light and used less power) but were later left in the dust by the much superior tungsten filament, which appeared in 1907 and was in widespread use for the next hundred years. See my other Edison GEM bulb. The higher wattage GEM bulbs (like this one) disappeared first, the smaller sizes were produced until 1917. This is why this bulb is so hard to find. The GEM filament is the work of Dr. Willis R. Whitney.
Westinghouse also made its own version of the GEM bulb, which was sold under the name "Westinghouse Metallized". It is interesting to note that GEM filaments are very springy, much more so than normal carbon filaments, and I suppose this extra flexibility might have made them more resistant to vibration. They appear more silvery than carbon filaments, and appear to be a thinner gauge for the same wattage.