Found these Exclamation Marks in an IGN Screen thought you might be able to make more sense of it than me. http://media.pc.ign.com/media/850/850126/img_4764227.html (Top Right of Screenshot) At first I thought it might be some kind of warning of an attack. Then I realized the Red Terran player had just used his Radar , so I thought they might have been revealed to him. Looking closer to the Exclamation points you can see the ground under color has been changed. So I came to the idea that it is most likely land mines.... thing is about that is Terran doesn't have any land mines to my knowledge... Any other guesses? My real question though is that if they are land mines what do they do( Other than explode) and how do they activate... and more importantly than both those, how did they get there? Enjoy 8) Changed the Wording a bit. Dug up gave the wrong idea I had for it.**
They had similar exclamation points in the video for when the sensor dome detected enemies in the fog of war... strange that they're here since it seems they can see that area. Unless perhaps the tall grass blocks vision? That would add tactical usage of the environment even more.
Yeah I believe those exclamation marks are the warning signs that allow your opponents to see where your sensor dome's vision has been placed. Do you see how the area where teal's units are slightly darkened? It could be the fog of war unless Blizzard has placed a weather system into StarCraft 2 complete with cloud cover and shadows, mmmmmm.
I agree that it is something to do with radar dome(not sensor dome). I'm guessing that it's more non-tank units from teal, such as marines. If you look at the two teal tanks in the shadow(probabaly FoW), they also have a red marking on each of them. I think perhaps they are revealed visually by the radar dome because they attacked from the FoW within the dome's AoE.