How to remove a rank on MW3 title from another Call of Duty game

This indicates their weapon proficiency. You unlock weapon proficiencies by gaining weapon experience getting kills with that weapon. This will unlock proficiencies such as Impact, Focus or the ability to use two Attachments.

For barrels and cars, you can tell that they will explode if they are flaming. Sparking fuseboxes etc explode only when they have taken some damage. This is true of all exploding objects. Observe a fusebox at the very beginning of a game. As you shoot it, it sparks and smokes more until it explodes.