When spray paint is allowed to sit on a bumper for an extended period of time it will damage the underlying paint. Any paint not part of the vehicle's original finish should be removed as soon as possible. Removing spray paint on a black car bumper can be done with simple automotive chemicals, if promptly attended to. Automotive chemicals must be used in an open, well-ventilated area in order to avoid inhalation or injury.
Wash the bumper with a dish-soap solution to remove any dirt, residue or wax.
Dry the bumper completely with a clean, lint-free towel.
Apply a white spirit, also known as paint thinner, to a clean, lint-free towel. Gently wipe the spray paint from the bumper using a circular rubbing motion. Do not rub vigorously. If the paint is not coming off easily, apply more white spirit to the towel.
Continue rubbing until all of the spray paint is removed. Apply a carnuba-based automotive wax to the bumper to protect it from future damage.