Smitten by the national rage "Kolaveri Di" sung by south Indian film star Dhanush, the Kolkata traffic police is literally humming 'Why this herogiri di?' these days, urging errant bikers to wear helmets.

In a novel idea to promote safe riding, the Kolkata police have put up signboards with the slogan 'Why this herogiri di?' across the streets in the city, asking bike riders to wear helmets and ride safely.

"During the year-end, bikers while enjoying themselves often do not wear helmets and ride rashly.

So we came up with this catchy line to attract the attention of errant riders," police commissioner R.K. Pachnanda said.

"We want them to be happy but at the same time they must follow the safety rules," he added.

The sign boards show two riders on a bike without helmets. Above them is written 'Why this herogiri, herogiri, herogiri di?' and below is the request to wear helmets.

The hoardings have been put up strategically across important and busy crossings and streets in the city.

Dhanush and composer of the song, Aniruddh, performed the phenomenal song in Kolkata on Christmas day amid thousands of screaming and cheering fans.