Hi Mark,
Sans serif doesn't just refer to block-type lettering (as opposed to cursive), but more specifically, to block-type lettering that is absent the little 'feet' you find at the end of each stroke on each character (called 'serifs').
In the image below, the word "ALPHA" appears in a serif font in the image below, while both the trademark on the left (with the heart & pistol) and the caption underneath are written in sans serif fonts:
With that in mind, what is the earliest example you have seen of an English knife that is stamped with a sans serif font?
Regards,
Chris