Copper cables by railway lines through St Helens in Merseyside are to be sprayed with a traceable liquid to deter thieves.
In the last 18 months there have been 19 cable thefts in the town. Network Rail said it had led to 250 hours of delays and cost thousands of pounds.
The SmartWater fluid, which marks the thieves' skin, has a unique signature which links them back to the crime.
The cables are stolen and sold for scrap.
Keith Lumley, from Network Rail, said: "If any of the cable is stolen and found in the possession of someone who shouldn't have it we can link back to the specific site.
"We hope this will deter people from committing cable theft attacks on the railway."
British Transport Police (BTP) has said in the past that it is a "major problem" for the railway community and the force has upped its patrols in many areas to catch the criminals.
Offenders also risk their own lives by stealing the copper as they often trespass on to the railway and could be hit by passing trains or electrocuted.