Here are some "M249s" in movies/TV shows that are actually Daewoo K3s made to look like M249s:
3000 Miles to Graceland:
Stargate: Atlantis
Walking Tall:
Also, note the front sight of the guns in "Walking Tall"; this is probably the best close-up I've found illustrating the difference. The front sight on the Minimi/M249 is a different shape from the side.