Everyone has a 6 yard circle around them. If two circles are overlapping that means that people are closer than 12 yards of each other and will share Blood nova.
Example circles and other markings in Ironforge.
People with Gas spores are clearly marked with a red circle. This also gives you the range for the aoe explosion soon to follow. Nearby players are also marked with smaller hexagons.
Everyone leaves a red circle on ground when the Big ooze explodes. This gives you a clear view where it's safe to stand.
