I can't advise you enough against metal polish on knives that don't have satin or mirror finishes. It destroys finishes and marks. On my Brian Goode Civilian, I have an O1 blade that he etched with ferric chloride (he used it to etch his maker's mark too). When I polished it very lightly and very quickly with White Lightning Metal Polish, the finish ended up ten times lighter, my hamon disappeared, and his maker's mark had vanished.
There is, of course, a happy ending- I went to Radio Shack, bought a 16 oz bottle of ferric chloride (it's actually pretty cheap), mixed it up about 1:3 with water, and re-did the etching with 10-second soaks at a time. The finish came out just like new, and my hamon was as visible as ever! On parts that you can't dip in the solution (like the handle so you don't damage the scales), mask off the scale and rub the ferric on with a cloth. I then neutralized the acid with ammonia and baking soda.
Once my finish was perfect, I put some undiluted ferric in the cap of the bottle and dipped a toothpick into it, then dragged the toothpick carefully over each depression in the maker's mark. Viola! Good as new.
This only works if your etched lettering is actually eaten into the steel. Ferric chloride is commonly sold as PCB (Printed Circuit Board) Etchant. It's only about $4 for a 16 oz bottle at Radio Shack, and at a 1:3 dilution that's 48 ounces of solution.
