[Jim McDougall]

Cathey, this is truly an anomaly, and you're spot on with the 'pioneer' attribution in my opinion. These 'saw back' weapons were key to these engineer units for utility in constructing field fortifications with trenches or defenses around artillery.

The cross hatching on the grip as well as the stepped pommel design remind me of the colonial cavalry sabers made by J Bourne & Sons under contract with Wilkinson for Indian military 1880s+. The one I have (pictured as were used by 13th Bengal Lancers), seems to have notable similarity.

Interestingly, the cross hatch ebony grip seems to have been a French affectation during about Napoleonic times for officers swords, so not sure what connection, if any, might be there.

The British saw back pioneer sword was introduced (officially) in 1856. It seems to have in some degree been intended for use by the artillery gunners for the utility purposes noted, and replacing the so called 'Spanish' style sword bayonet they were apparently using during Napoleonic period. That term is claimed to have been colloquial for its use in the Peninsular campaigns in Spain.
Burton (1884) noted that these 'saw backs' were pretty much useless as either tool or weapon, and as a bayonet was worse as the serrations would cause the weapon to be hopelessly lodged in the victim.
Still this feature seemed to prevail, and by WWI the Schmidt-Rubin saw back bayonet used by the German's was seen in that terrifying view, so much so that it was said that British soldiers capturing Germans with these 'barbarous' bayonets would shoot them on the spot. The Germans in response, began grinding down the backs of these.