Tombstoning is when people jump unsupervised into the sea from places including cliffs and harbour walls.
Maritime and Coastguard Agency figures show 189 tombstoning-related incidents were recorded between 2004 and 2009.
Steve Wills, from the RNLI said there had been at least five deaths from tombstoning.
BBC: NEWS | UK | England | Cornwall | Group teaches 'safe' sea jumping
He tells his story in a new video by the RNLI warning of the dangers of tombstoning.
Mike Puplett, watch manager for Humber Coastguard, warned about the dangers of tombstoning.
Mike Pulpett, watch managed for Humber Coastguard, warned of the dangers of tombstoning.
About 20 signs stating whether people have been killed or injured from tombstoning in the area will be put up.
Warning signs are being displayed at tombstoning hotspots in north Cornwall in a bid to reduce serious injuries and deaths.
Across the UK in the past five years there have been 18 fatalities and 57 serious injuries from tombstoning, the MCA said.
Granting the order, the city council said it would allow police to tackle anti-social behaviour associated with the activity known as "tombstoning".
BBC: Groups of tombstoners in Devon targeted by police order
Sonny Wells, 22, broke his neck when he jumped off South Parade Pier in Southsea in 2008 - a practice known as "tombstoning".
Incidents recorded by HM Coastguard show since 2007 there have been at least 14 deaths and 40 serious injuries nationally due to tombstoning.
New laws have been enforced by an East Yorkshire council to try and combat people jumping into the sea from a height or "tombstoning".
Matt Pavitt, from north Cornwall MCA, said there had been a rise in the number of people tombstoning across the UK in the past two years.
The RNLI has campaigned against the tombstoning craze.
BBC: NEWS | UK | England | Cornwall | Group teaches 'safe' sea jumping
During the past five years in the UK there have been 139 tombstoning incidents needing an emergency response, with 12 resulting in fatalities and many more resulting in spinal and limb injuries, according to the Royal Society for the Prevention of Accidents (RoSPA).
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