This symbol for in vehicles

BF4 uses a "smart lean" system. The beta is a bit buggy with it, but the premise is that when that pops up, you are by a corner and holding the ADS button will cause you to lean around that corner, exposing less of yourself to the enemy. The best way to see it is to stand at the corner of a wall and play with it. It takes some getting used to but once you do, it will feel smooth.

It is the zeroing mechanism. This means that if you have it zeroed at 500m, the cross-hairs are dead on at 500m. This allows you to make distance shots much easier. If you were to zero the scope at 500m and shoot at a target at 100m, your shot would hit much higher than your cross-hairs. Previously, your only option was to compensate for bullet drop by aiming high and guessing between mil dots, which made distance shots on moving targets much more difficult. If you have your scope properly zeroed, now you can just offset the horizontal reticule the appropriate lead for motion.