In heraldry, a "roundel" is a circular charge. These include the escutcheon or inescutcheon, lozenge, fusil, mascle, rustre, billet, roundel, fountain, and annulet. Its logo was a water wheel above the London Transport roundel. Its logo was a squirrel above the London Transport roundel. Inmates assigned to it wore a black roundel bordered white under their triangle patch. It was carried on a prominent white roundel on each sponson, underneath an infinity symbol. The Romanian roundel uses the colours of the Romanian flag. Originally, the air force used the red, white and blue roundel of the RAF. The Sabres were among the first to wear the RAAF's recently introduced "leaping kangaroo" roundel. The simple flat gravestone lies north-west of the central roundel within the main avenue. Most uncamouflaged training and transport aircraft retain the traditional red-white-blue roundel. The London Overground also uses a variant of the TfL roundel. The Serbian Air Force roundel was officially adopted in 2006. The current RCAF also uses a low visibility tactical grey roundel. This roundel in particular depicts the King of Christmas.