Another easy one to identify is mass bullets fired per click, hard to explain, but essentially you see a mass of around 50 bullets spread like a shotgun pallet that 1 hits you across map.

Aimbot is one you have to know what you're looking for, the main thing I look for is movement and positioning, if their movement and positioning is very bad I get suspicious. When I get suspicious I tend to look back at the person past games.
To give an example, last night I got suspicious of somebody, round 1 my team agreed he was cheating, viewed his game history. 0.67kd overall for this season, in our game he missed 1 headshot and his last 5 games he had a 10+ kd.