Call of Duty 4: Modern Warfare/HUD

Objective Indicator
On the bottom of the picture is the compass. As well as giving you directions you'll see green triangles and red circles. The green triangles represent your team mates and the direction of the pointy end of the triangle is the direction in which they're facing. The red circles represent your enemies, but only if you can see them or they're firing. If an enemy is behind a crate or another obstacle and is not firing or creating any noise, then it won't be shown on the compass. The star on the compass represents the direction of your objective. So if the objective is to blow up a tank, then the tank is in the direction of the star. If the objective is to secure a building, then the direction of the building you need to secure is shown by the star.

Ammo Gauge
On the bottom right is the ammo gauge. The lines show you how many bullets have been loaded into the gun, the numbers show you how much ammo you have left in total. When you press the reload key or run out of ammo, it will automatically reload.

Grenade Gauge
Slightly above the ammo gauge but still in the bottom right corner is the grenade gauge. It shows how many special and frag grenades you have. You can only carry 4 of each grenade at the same time, but the number gets renewed every time you complete a mission. Occasionally, you will find grenades on tables, when you go near them they will automatically be added to your total if you have less than 4.

Text
In the top left corner there'll occasionally be messages like "Objective complete" or "Checkpoint reached". Once an objective has been completed you'll also see details of the new one in this area of the screen too. In the bottom left of the screen, only at the start of every mission, only there will be details of the mission (name/place/date). You may also see dialogue from your allies at the bottom of the screen.

Grenade Indicator
This will point to wherever a grenade has landed. If you see one of these then it means the grenade could potentially kill you. You can get move to get behind cover (you may still see the indicator), run away or get nearer to the grenade and throw it back.

Grenade Throwback Indicator
If a grenade lands very near you, you have a chance to throw it back. This is normally better than running away as throwing it back if faster. You should immediately throw it back as you may not know how long the enemy cooked it for. They also do not seem to throw grenades back often.

Damage Indicator
When hit, a red arrow shows the direction of the soldier who hit you. If you are hit repeatedly, your screen will turn red and you will be able to listen to your heart beating and heavy panting. If this happens, you are seriously hurt and need to take cover to replenish your health.