Ads resembling graffiti by US footwear giant Nike have provoked protests in ultra-tidy Singapore.

About 50 people wrote to complain that the city's usually immaculate bus-stops had suffered acts of "vandalism" or "graffiti" after 700 posters featuring US basketball star LeBron James went up, Singapore media reported.

Graffiti is a sensitive subject in the wealthy island known for obsessive civic orderliness.