In the middle south of Karachi is a stone wall that runs north/south with an arched doorway in the middle.

If you approach from the eastern side, follow these steps to get over it;

Look at the archway, look left at an orange scaffolding. The left crossbeam is levitating in the air. Look left at sandbags piled up. Look left at a small chicken cage (occupied) on the ground across the aisle from the sandbags.

Jump onto the chicken cage, jump onto the sandbags (the green roof may get in your way a little, go slightly right to get around it), jump onto the levitating crossbar and climb the scaffold. Turn around and jump onto the top of the pole that is up against the wall (the horizontal beam isn't real, jump onto the top of the pole). Face the wall about 2 bricks in from the right edge. Jump forward and you should slip up top. This is quite easy with practice.

Karachi sign extra: Read the post on Karachi sign spot- Get on the highest red letter on the left (looking at the sign from the cafe), face the wall behind you and jump and crouch to get into that long window up high. Move to the edge of the map and snipe from up there.