The Notice skill involves just that—noticing things. It’s a counterpart to Investigate, representing a character’s overall perception, ability to pick out details at a glance, and other powers of observation. Usually, when you use Notice, it’s very quick compared to Investigate, so the kinds of details you get from it are more superficial, but you also don’t have to expend as much effort to find them.
You don’t really use Notice to overcome obstacles too often but when you do it’s used in a reactive way: noticing something in a scene, hearing a faint sound, spotting the concealed gun in that guy’s waistband.
Note that this isn’t license for GMs to call for Notice rolls left and right to see how generally observant the players’ characters are; that’s boring. Instead, call for Notice rolls when succeeding would result in something interesting happening and failing would result in something just as interesting.
Create an Advantage:
You use Notice to create aspects based on direct observation—looking over a room for details that stand out, finding an escape route in a debris-filled building, noticing someone sticking out in a crowd, etc. When you’re watching people, Notice can tell you what’s going on with them externally; for internal changes, see Empathy. You might also use Notice to declare that your character spots something you can use to your advantage in a situation, such as a convenient Escape Route when you’re trying to get out of a building, or a Subtle Weakness in the enemy’s line of defense. For example, if you’re in a barroom brawl you could make a Notice roll to say that you spot a puddle on the floor, right next to your opponent’s feet that could cause him to slip.
Notice isn’t really used for attacks.
You can use Notice to defend against any uses of Stealth to get the drop on you or ambush you, or to discover that you’re being observed.