In Montana, where I do most of my elk hunting, the presence of a brow tine is the definition of a legal bull in many hunting units. This is the first thing I look for. If I can't see a brow tine, I'm almost certainly not looking for additional features. But if it has a brow tine, I look at its length (as long as its nose, and it's an old, trophy-class bull) and its mass. If the mass of its base extends well out the brow tine, then it's probably a 300-plus-inch bull. There is an important disclaimer, though. Once, in the Missouri River Breaks, I spied a huge 6-point and stalked in for a closer look. His right side was massive. But his left rack was nothing but a long, distended brow tine. It looked like a war club. If I had based my assessment of that bull only on the left tine, then I would have ended up with a 200-inch bull, 150 inches on his right and about 50 inches on his left.
If I can't see any other part of a bull's rack, I will seek out a glimpse of his fourth point. If it's long and massive, it's almost a certainty that he's a mature bull. Also called the dagger point, the fourth point will imply size and points. As the RMEF correctly notes, if you see only one point above the dagger, then it's probably a 5-point bull. But if you can see a Y above the dagger, he's a 6-point, and you can start looking at other features to assess his trophy potential.