The non f cast cabers are pretty dark like that and aren't marked.
Those look like they could easily be cabers, need a closeup pic of the ring edges to be reasonably sure.
This is the easiest way to tell they're caber, the machine marks and more importantly, the beveled edges.
Not the best pic for this, the bevels are normally very obvious, the machine marks aren't always this obvious and you need decent magnification to see them.
I don't know of any other brand that looks just like 'em...
<EDIT>
This pic is the standard non f cast caber.
The machine marks aren't so apparent on this type but it shows the characteristic bevel with the slight ridge/burr on top. Bevel is on the both the outside top and bottom.
If the OP's, are fake or misrepresented as caber, it's the first time I've heard of it...
I've had a piston that was supposed to have cabers come with other than but they certainly weren't in a caber box.