Isn't that Russian red star on his shoulder from back when he was being used as an assassin? Why's he keep it?

He actually didn't. SHIELD gave him a new arm with a different symbol on it.

@xwraith: In his solos Winter Soldier, and Bucky Barnes it's a red star again.

@ghostpiratex: The best explanation I can think of for that is an error on the artist's part. Either that or Marvel went back to it because it's in the movie.

Yeah, I'm not sure why they stopped using the red, white, and blue star that his arm had during Brubaker's run. My best guess is that it's an error on the artist's part or that Marvel is trying to make him resemble his movie-counterpart more who still had the red star on his arm.

Personally I'm always annoyed that he's currently sporting the red star, which he stopped using after he lost his bionic arm the first time during the Red Menace storyline. After that he sported a simple white star on his arm until around the time Steve Rogers was killed and Bucky became the new Cap, after that and all the way up until the end of Brubaker's run on Winter Soldier Bucky sported the Cap shield star on his arm. After the Black Widow Hunt storyline Bucky sported a black star that had a red outline in honor of Black Widow who Bucky had lost follow that storyline. Now he's sporting the red star again in his current series, which is most likely due to Marvel and/or the artist wanting him to resemble his movie-counterpart more.