Abstract: The present invention provides a method for providing a cautionary warning on water-going vessels. The method comprises the step of placing a plurality of reflective warning markers on at least one side of the vessel. These warning markers preferably comprise a front, reflective (that is, reflecting incident light) surface and a rear surface. The rear surface comprises an attachment mechanism adapted to attach to the surface of the side of the vessel. Preferably the attachment mechanism is coextensive with at least the perimeter of the front, reflective surface. The present invention also provides a removable informative marker. This marker comprises a resilient, front reflective surface and a resilient, back magnetic surface. The resilient back magnetic surface is preferably substantially coextensive with at least the perimeter of the resilient, front reflective surface to assist in assuring a firm attachment of the marker to a metallic surface.