The advertisements printed on umbrellas are generally oil-soluble paints.

you can use natural water, that is, "natural water", "banana oil" and "acceptable water", also known as banana oil, also known as diluent.

is a mixture of a variety of organic solvents in a certain proportion. It is volatile at room temperature and has a strong banana smell. It is toxic and is mostly used to dissolve paints and adhesives.

you can also find some gasoline and wipe it. it should drop easily.

so you don't have to worry about those colorful signs.