Every time I'm playing on Normandy I tell people there is a enemy in that house in d4 (this is an example)
and they say which one? And I can't really be very specific because I died and was inside the house, so I'm not sure which house exactly.
And so I thought, what if we had some sort of grenade or something that would let them know which one.
I was thinking maybe a strobe light that only your team could see and and it would flash every 1 second or so, almost like the tactical insertion does in Black Ops, and you simply select it aim at a area you want to mark, and fire it.
It would stick to the wall or ceiling and flash, maybe then your team would know where to look.
And to avoid spam, you can have 3 per life and they don't go away after death but when you respawn and fire another, it removes one of the others that you fired before.
Maybe it could look something like this

Just a simple idea I though up.