What you use for engraving depends on the required results, to get sharp corners on small letters you will need conical D-bit cutters and V-Carve type cutting paths, interestingly some V-Carve implementations allow use of a slot drill/endmill to rough out areas between sections requiring the tapered cutter.
Conical cutters inevitably yield sloped sides, if the job requires vertical sides on the engraved features then small slot drills/endmills will be required.
I've done work in brass with endmills down to 0.6mm with spindle speeds at 28,800 rpm and above, a good feed & speed calculator becomes vital here as minimising tool deflection is as important as anything else in generating a working tool path and maximising tool life,

- Nick