I have done a lot of work on lathe legend plates of different makes and models of lathes. What I have found that works the best for me is just a plain old pencil eraser to clean and polish the brass edges and raised lines between letters and numbers. Be aware that the color in your legend plate is enamel. Not paint but rather a process were after the plate has been embossed so there is a low area were the color will go an enamel powder is applied. Then the plate goes through a baking process to turn the powder to a liquid and then a solid. Much like powder coating. This material is much more abrasive resistant than paint would be. After the baking the plates are passed through a buffing machine that just touches the high points of the plate and buffs off any remaining enamel and polishes the brass. By using a pencil eraser I have been able to clean and polish the brass without getting into the enamel. Then I use an aluminum polish called Simichrome to put a shine on the plate. Then I wash the plate with good hand soap and blow dry and then I give it a coat of clear urethane. This is the way I have done all the plates you see on all my lathes. First you need to have a good plate to start with. Some of the cutting oils in the past would attack the enamel and that is why we see some plates that have no color on them at all. The problem of re-applying the enamel is the plate needs to be very flat to do a good job and most of our plates are a long way from being that flat. Hope this helps a little.
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Dennis Turk