In this poster, there is dun’s which is a reference to the classic mission: Impossible theme song. Most spy movies take place at night which is represented by the lamp post. The security guard is there to show that the building is a guarded place. Most of the places the spies try to get in to are heavily guarded. There is also a man in a suit with a gun looking as if he is ready to shoot. This is a very genetic thing seen in most spy movies. You can see it here in the kingsman movie:
The key things in a spy movie are that they have big/dramatic openings which help lure the audience in. They also have incredible action scenes with many twists and turns throughout the whole plot. Last but not least the MacGuffin which refers to a goal that the protagonist is tasked with pursuing to further the plot. The poster show this by the guy looking as if he is ready to shoot.