Slightly O.T. Cutting tool trademark

What cutting tools company uses OK inside of a diamond shape?

They are out of business, but "OK". I know them more for special tool shapes with serrated mounts, basically HSS indexable tooling, than for plain square or rectangular tool bits. But you only said "cutting tool" with no photo.

I hope this helps. The cutters are not very photogenic.

Right. Those are from OK. I don't know what, if anything, OK might stand for. People familiar with them are likely to refer to them just as "OK".

You have the kind with shanks rather than serrated mounts. I believe cutters of this style were more commonly used on shapers and planers, with a toolholder bar with (obviously) a shank-sized bore in the end. I'd have to see better views of the working ends to tell you for sure whether these were lathe tools, or planer/shaper tools.

Here are a few (transient) links to an OK catalog (1911, but they were made into at least the 1950's, possibly longer), a toolholder with one cutter installed, and a set of shaper/planer bits with toolholder.

1911 Catalog
Toolholder with one cutter
Set of shaper/planer cutters

And I've saved some of the images, since those links won't last.

Note: there were a couple of different ways to lock the cutter shanks in the toolholder. The toolholder for the set has a drawbar, while the single toolholder has a cam (I think).