Systems and methods for determining the cleanliness of a surface. Surface marking systems of the present disclosure can include a plurality of retroreflective microspheres dispersed in or dispensed on a carrier. Applicators of the present disclosure can include a container comprising the surface marking system, and a dispenser. Methods of the present disclosure can include applying the surface marking system to at least one discrete site on the surface； illuminating the at least one discrete site on the surface with visible light, after a cleaning； and detecting retroreflection emitted from the at least one discrete site on the surface in response to illuminating the at least one discrete site to determine the effectiveness of the cleaning of the surface.
