I recently came across a series of well done DC Comic covers for Rush City (the cover of issue #6 is above) which were simply credited "Cover by Jock". It took me a bit of creative googling, but it turns out Jock is the pseudonym of British comics artist Mark Simpson, known for his work with Andy Diggle on the science fiction comic book 2000 AD and on The Losers. His website is well worth a visit: