in 2002, Canada won the hockey championship from the Olympics, to celebrate, they buried a Canadian loonie (1 dollar coin) in the snow in an area that never melts, now, in Halo 3, on the level 'snowbound' when you enter the tunnel to get active camo, look around the ground where the camo is, (with a sniper works best)
You should see a gold coin partially buried in the snow, that looks exactly like the pic of the loonie I posted.
CPO’s nerdness kicks in: This obviously means that forerunners are Canadians and they took direct sample of snow from canada!