I think most logos are acid-etched or 'electro-etched', to produce a dark oxide layer which forms the logo. Depending on how strong the etch was, and/or how deeply oxidized the steel is, some logos might be easier to remove than others.
Assuming it is an oxide layer, that can often be polished away with products made for polishing hardened steel. Flitz and Simichrome might work, as should other polishing compounds like silicon carbide, aluminum oxide (Flitz/Simichrome use it) or diamond compounds. Most etches will still take some additional time and 'elbow grease' to remove, even with these compounds.
Some more modern/high-end knives have deeply lasered etches on them (Spyderco etches their 'bug' on the blade like this). If viewed under magnification, the laser leaves a pattern of closely-arranged 'dots' or deep pits in the steel. Those won't be removed by polishing alone, but instead would have to be sanded or ground away by much more aggressive methods.
BTW, sanding with wet/dry sandpaper will obviously remove the shallower etched logos, but that may be overkill for many, and will leave a whole new pattern of scratches behind.
David
