Sharpie markers are AP-certified as nontoxic by the Art and Creative Materials Institute. However, the markers are not meant for use on items that come into direct contact with food, drink or the mouth.
When Sharpie markers are used on a cup or mug intended for actual use, the design should be placed at least an inch below the spot where lips would come into contact with the item.
Sharpie markers are not intended for use on skin but are not harmful in small amounts. The ink wears off on its own after about two days. Alternately, rubbing alcohol, acetone or vinegar can be used to remove ink marks from the skin.