Liberty is wrong. They are actually quite simple to remove, assuming you are talking about the white mark left behind on wood finish or stain. Here are some steps --
1. Spread about 2 Tablespoons of mayonnaise on a paper towel.
2. Place the paper towel on the white water mark. Press lightly.
3. Leave the mayonnaise on the stain about 15 minutes.
4. Lift the paper towel and check the stain. If the mark remains, rub more mayo into it again and check it later.
5. Stain should be gone. Reapply if necessary.
There are a few other tips if that doesn't work to be found here:
You can't, but if you're wanting to hide it from someone, put a lamp or coaster or rug or something to cover it up.