This is the icon for the Warhorn. It is an antenna with waves coming out.
Hypothesis:
The antenna suggests to me that the warhorn is comms related, and the waves emitting from it is the result of sending a signal.
Given the amount of possibilities that this could be, I suspect that this device will likely be used to ping yourself on teammates minimap when you need help, followed by an audible warhorn sound. It could potentially make use of the ray-tracing feature from your reticle to place a HUD marker pointing to the targeted location. This can help players warn other lance or team mates without being the commander of either. No order will be given, but it can be used effectively to draw the attention of others to areas of greater threat.
Likely similar to a spotting feature that is used in Hawken. At the press of a button, it lays a red blip in the minimap and an icon in the HUD to show the area where an enemy as been spotted. The advantages of this help players communicate quickly without the need to type; something that PGI is working towards, along with mention about a command wheel to easily command or communicate with your team.
Some things in question:
However, one downfall is that there is no positional audio in MWO(surround).
Quote
Only effect that exists is a a crude version of muffled sounds based off proximity, and stereo effects per individual sound. You will not be able to tell in which direction the Warhorn was used.
Also, we aren't sure yet if Warhorns are Clan specific or not; I made the assumption that it is not.