We do not recommend painting on unpainted surfaces. Painting over surfaces like stucco or brick can make them difficult to maintain. Always try to remove graffiti from unpainted surfaces rather than painting over them.
Read about removing graffiti
Do not "picture frame" graffiti. If you cover graffiti with a block of paint in a different color from the original exterior paint, you will create a "picture frame" noticeable by vandals. This could make your property a target for future tagging.
Paint entirely over the graffiti. Do not just trace over the letters or symbols with paint. Apply matching paint in a square or rectangle larger than the tag and blend the edges.