This is quick in game, but quite complex to understand. This allows quick landing/drop of supplies from friendly helicopters and can help avoid the helo coming under heavy fire and losing 10 tickets for your faction.

1: Get your T commo-rose selected and press the 'NEED SUPPLIES' label. This will inform friendly choppers who you are and that you need supplies.

2: Immediately start transferring this information to the pilot(s):
*You're location via grid reference and KeyPad.
*The recommended approach vector. This is the direction you want the helicopter to approach the LZ from
*The recommended exit vector. This is the direction you advise the helicopter pilot to leave the LZ from.
*Inform the pilot whether he will be landing under a green, yellow, or red LZ. these codes will be explained later.
*OPTIONAL* Tell the pilot his actions upon approaching/leaving the LZ. Such as popping flares every 5 seconds or coming in fast and low. These should only be used when the LZ is being engaged or when enemy units have view of the LZ.

3: Pop smoke on LZ and inform pilot what colour smoke you have placed down.
*This is to make insertion easier for the pilot, the smoke can be seen from a good distance away and it makes it easier for the pilot to locate the LZ. Making it a quicker insert.

LZ CODES:
*These are taken from Zedic's "Military Radio Procedure Adaptation" thread in the Tactical Gamer Project Reality forums.

LZ GREEN:
*This means that the LZ is clear of enemies and is receiving no incoming fire. This will advise the pilot that he can act a bit more freely upon performing the logistics mission.

LZ YELLOW:
*This means that the LZ is receiving sporadic fire. It advises the pilot that he may be engaged with small arms when he reaches the LZ. And since the pilot will know he'll be landing under light fire, it will make him more prepared when he does take fire.

LZ RED:
*This means that the LZ is in contact (effective suppression) and is heavily engaged. This will advise the pilot that he will come under heavy fire, possibly by high caliber weapons and small arms. Since the pilot will know that he will be landing under lots of fire, it will make him more prepared when he does take fire. When the LZ is red it is advisable to tell the pilot your recommended actions when he enters/exits the LZ area.

When things go Wrong:
If something happens during the pilots approach to the LZ, that could possibly mean the helicopter be destroyed/disabled and/or the pilot killed. The main information to convey is "ABORT" followed by why you need the pilot to abort the logistics (supply) mission. Telling the pilot why is a simple precaution if the pilot did not hear/see the "ABORT" message. Because if you tell him, for example, there is an AAV watching the LZ, it will jog his memory that Helicopter vs AAV = -10 tickets and -1 Chopper for your team.

Infantry actions during Helicopter's approach on LZ (with code discipline):

Infantry defence on a GREEN LZ:
*The infantry should set up a perimeter overlooking the 4 main compass directions (North, East, South, West). They should remain in a prone position to keep the LZ a bit more secret from the enemy. Also, the infantry should constantly scan their specific area for any contacts and keep at least 20m from the LZ.

Infantry defence on a YELLOW LZ:
*The infantry should set up the main of their force looking out for the shooters putting fire on the LZ while the rest of the infantry scan the perimeter. Because the LZ has been spotted, it's recommended the scanning infantry keep moving or stay in cover (while still in good view to scan) to avoid getting hit and thus losing their perimeter scan ability to receive medical aid. The infantry should also keep a 50-70m distance from the LZ.

Infantry defence on a RED LZ:
*The infantry should look to suppress the targets with heavy weapons (e.g. SAW's, Marksman etc...) while the lesser roles (e.g. riflemen) keep the LZ secure. It's recommended that the infantry keep to cover and (if possible) keep mobile to avoid getting hit and losing their ability to perform their specific LZ defense duty (I.E. suppression, perimeter scan). It is recommended the infantry keep a 70-150m distance from the LZ to avoid attracting attention to the friendly helicopter entering the area.

That's about it. Hope this thread gives you some insight on how to best organise a supply drop from a helicopter as an infantry SL.
You could speak to the pilot directly via mumble/TS. Or use the team chat or CO to convey the message. It is a lot easier to use radio like TS.