A pantograph machine would cope with a flat or domed top, we used a Gravograph IR3 machine for engraving bowls for a nearby sports shop among other things. We and many others were reluctant to take on 'one off' jobs, particularly on the customers own property, there's nothing like slipping out of the brass copy on the last line of a multi line engraved brass plate!
I do have a Gravograph IT4 machine, a restoration project for the future sitting on my bench, sadly no copy and the cylindrical engraving parts are missing, otherwise, I like a challenge!