Pc Jim Abram and Luis Tulip
Police and cycle shops are marking the cards of criminals thought to be behind the city's illegal bike trade.
A Green Card system began in 1980 and eight of the city's main cycle shops were signed up.
The scheme was relaunched at Beeline Bicycles in Cowley Road last month.
A cyclist must now have a green card issued from St Aldate's police station to prove ownership before being allowed to sell the bike to a local shops.
Pc Jim Abram, of the cycle team said: "We are working hard to foil the bike thieves."
Luis Tulip from Beeline Bicycles said: "It gives us the security to purchase second hand bicycles."
A register of bikes and owners is kept at St Aldate's police station.
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