Sometimes a logo is painted on a product.
Ink is very good for covering unwanted images on lots of different types of material.
A black marker is good for covering over images where the product is also black, but it doesn't work as well when the background is a different color. I have yet to experiment with other colored markers.
Some surfaces, especially some paperback book covers do not seem to accept ink well. In these cases, I have tried applying an adhessive sticker to the surface, and then coloring that, but it looks a little cheesy.
In general, you should look into the methods described in the removing logos method before reaching for the marker. It is always more elegant to remove the logo entirely than it is to merely cover it up.
Color over the image you don't want to see with the marker.
Repeat as needed, once the ink as drie.
Sometimes two or three coats are needed.
Remember to use your markers in a well ventilated area.
Also do not use of food packaging, since ink is toxic.
Black markers are not hard to find, and most any type you can get will work fine. It would probably be better to get one which claimed to be waterproof though.
List out any methods that use this tool.
Provide links to the methods from the methods section.
The ability to color within the lines !
Easy to implement, but not worthwhile doing if the ink doesn't match the background of the product. It's also a bit messy, since the ink tends to get on your hands.