?

I've been led to believe that lettering or inscriptional lettering in this style (ie. monoline, thin sans) did not exist that far back. Or have I misread something?

The possibility of a lazy stonecutter might explain a lot...

I have no elements to agree or disagree. What I note: it tries to keep Trajan proportions and uses old Roman abbreviation system. Memento mori is Latin for "Remember you will die". Die is "day" and after 27 the word faded probably indicates the month in Latin numerals.

The fact that this is cast iron leads me to believe that it is genuine. Imagine the technique required to produce this if it were done with a sand form. The craftsman would use a template (a blank slate with bevels and such), and paste the letterform onto that (maybe using rolled bits of clay — tightening up forms as needed wit a quick slash of a knife). Makes it feasible that doing serifs and other refinements was out of the scope of the persons’ capabilities or even not very economical.
Master pushed into sand. Melted iron poured into that. Presto.

@oldnick: Stone doesn’t come into this : )

Anecdotal: sans styles have been around before serif styles…

That makes a lot of sense as an explanation. I'm surprised there aren't many more "sans serif" letters from that era though.

I do really like the Roman proportions on this, it makes it feel very 1920s neoclassical. :)

Metalsmiths can be lazy, too...

The memorial could have been created years/decades/centuries after the subject died.