Two bodies found near railway lines in Hertfordshire are among 20 dead people police are hoping to identify using artist's impressions.
The two men, one found in St Albans in 1995 and the other in Harpenden in 2004, had both been struck by trains.
British Transport Police believe the men and 18 others found near train tracks in the UK in the past 35 years were not victims of foul play.
About 200 to 300 people are killed on the UK's railways every year.
Two swallows tattoo
Det Ch Supt Miles Flood said: "It is likely there are still relatives who may recognise them and thought they had moved away."
A man aged about 30 was struck by a train at St Albans on 2 August 1995. He was about 5ft 7in tall with brown collar-length hair and was wearing a blue T-shirt, grey trousers, and brown boots.
He had a tattoo on his right forearm featuring two swallows holding a banner with the words "Marie" and possibly "Ena".
A man struck by a train at Harpenden on 19 August 2004. He was 25 to 35 with a shaven head.
He was wearing a green camouflage sleeveless shirt, black jeans and black trainers.
Artist Sharon McDonagh used mortuary photographs to create most of the sketches but had to use an image from CCTV footage of the man found at Harpenden.