Try a scotchbrite-type pad. GW thread--Poof! Marble etch gone.

There are many threads on etched marble, if you type that in the 'Kitchens' search field.

Etching is a physical damage to a stone. It's not like a stain which can be removed. In a bathroom, you will get more etching over time. Things that will etch marble include drips from toothpaste, mouthwash, perfume, acne medicine, anti-wrinkle creams, some soaps. This is the nature of marble, and you cannot change that. Eventually your eye won't notice this etch, or the others. My advice is to wait a few years for a whole bunch of etches, and then hire someone to repolish the counter.

Mild etches can be blended with polishing powder, a scouring pad, a high-grit sanding sponge, or high-grit sand paper, depending on the roughness of your hone. My marble is honed, but hand polished to a nice sheen, so I use a damp sanding sponge, or the sponge combined with alumina powder.

No need to wait until your counter is covered in etches, if it makes you feel better to take care of the etches as they happen. I did that for several years, but as Shannon_WI mentioned, with time the etches don't bother me as much. It could have something to do with a deep, linear etch, which happened when juice leaked from a grandson's metal lunch box, and sat overnight. That was my island top's 'baptism by fire', and no other etch can compare. ;)

Thank you-I always forget to search! It worked!