As Medic, is there an indicator to know which of your teammate is asking ammo?

Yes, they will have an ammo icon on top of their heads instead or the usual blue or green circle.

Also note that if you hear that request, they’re probably not far: you could also just drop the ammo bag where you are, they will see it on their mini map. 

I see. I thought those ammo icon on heads mean that they are the ones who can provide ammo.

Ha, welcome to the confusing world of the BF6 UI: if you are ANOTHER class, and YOU need ammo, then that icon tells you who can give it. 

Note you're also supposed to be able to get ammo from a support player by pressing the action key. I've never got it to work though. 

>Note you're also supposed to be able to get ammo from a support player by pressing the action key. I've never got it to work though. 

I can get ammo from support doing this if they stand still long enough, half the time i chase them around and try to get ammo and end up getting killed before I can interact with them :/  also this does not resupply gadgets or grenades

Yeah, I actually checked a bit online after writing what I did: people are saying you have to long-press the action button, so that support needs to stay in place long enough. 

I know you can ask for ammo and health, long press a button (I’m on pc and I changed it so I don’t know the default) and it will open a wheel of choices: ask ammo, health, thanks, use spray etc.

So as Medic, that icon means they need ammo.
If other Class, that icon means they provide ammo.

Thank you.