Try isopropyl alcohol. It’s regular off the shelf product as a
dilute solution of alcohol and water. This should be enough to remove
the Sharpie. It contains a 60 - 70% water to alcohol mixture which
should be enough to remove the Sharpie but not hurt the plastic.
Another good solvent is 140 proof Grain Alcohol or pure ethanol
which you can purchase in some liquor stores. I didn’t know they sold
this in stores, but it actually works very well. It’s flammable, so
The following is from Wikipedia which is a great source for
Neutral grain spirit (also called pure grain alcohol [PGA], or grain
neutral spirit [GNS]) is a clear, colorless, flammable liquid that is
distilled from cereal grain and has a very high ethanol content. The
term neutral refers to the fact that it lacks any flavor derived from
the mash used to distill it, nor does it have any flavor added to it
after distillation (as is done, for example, with gin). The grain
from which it is produced can be any of the common cereal grains.
Other kinds of spirits, such as whisky, are distilled at lower
alcohol percentages in order to preserve the flavor of the mash.
Denatured alcohol is ethanol which has been rendered toxic or
otherwise undrinkable, and in some cases dyed. It is used for
purposes such as fuel for spirit burners and camping stoves, and as a
solvent. Traditionally, the main additive was 10% methanol, which
gave rise to methylated spirit. There are diverse industrial uses for
ethanol, and therefore literally hundreds of recipes for denaturing
ethanol. Typical additives are methanol, isopropyl alcohol, acetone,
methyl ethyl ketone, methyl isobutyl ketone, denatonium, and even
(uncommonly) aviation gasoline.
In the phrase denatured alcohol, denatured means “a specific
property of ethanol, its usefulness as a beverage, is removed”. The
ethanol molecule is not denatured in the sense that its chemical
structure is altered.