Article: The Canadian football field is 150 yards (137 m) long and 65 yards (59 m) wide with end zones 20 yards (18 m) deep, and goal lines 110 yards (101 m) apart. At each goal line is a set of 40-foot-high (12 m) goalposts, which consist of two uprights joined by an 18 1⁄2-foot-long (5.6 m) crossbar which is 10 feet (3 m) above the goal line. The goalposts may be H-shaped (both posts fixed in the ground) although in the higher-calibre competitions the tuning-fork design (supported by a single curved post behind the goal line, so that each post starts 10 feet (3 m) above the ground) is preferred. The sides of the field are marked by white sidelines, the goal line is marked in white, and white lines are drawn laterally across the field every 5 yards (4.6 m) from the goal line. These lateral lines are called "yard lines" and often marked with the distance in yards from and an arrow pointed toward the nearest goal line. In previous decades, arrows were not used and every yard line was usually marked with the distance to the goal line, including the goal line itself which was marked with a "0"; in most stadiums today, the 10-, 20-, 30-, 40-, and 50-yard lines are marked with numbers, with the goal line sometimes being marked with a "G". The centre (55-yard) line usually is marked with a "C". "Hash marks" are painted in white, parallel to the yardage lines, at 1 yard (0.9 m) intervals, 24 yards (21.9 m) from the sidelines. On fields that have a surrounding running track, such as Commonwealth Stadium, Molson Stadium, and many universities, the end zones are often cut off in the corners to accommodate the track. In 2014, Edmonton placed turf over the track to create full end zones. This was particularly common among U.S.-based teams during the CFL's American expansion, where few American stadiums were able to accommodate the much longer and noticeably wider CFL field.

Question: What part of a Canadian football field was sometimes marked with a "G"?
goal line