"Hidden Signals" is a two stage event, in which you will defeat Loyalist Camps to try and decipher the location of hidden boss units. Defeating these bosses will grant you amazing rewards!
First Stage: Collect Signal Fragments
In the first stage of this event you can defeat Loyalist Camps which have a chance to drop a special item, called Signal Fragment.
You need to collect enough of these Signal Fragments to decipher the location of the hidden bosses.
Not all Loyalist Camps will have a chance to drop a Signal Fragment. Depending on your HQ level, certain levels of encounters will have no chance to drop this item. Look for the Signal Fragment's icon in the reward pool of the encounter's contextual menu to make sure that encounter has a chance to drop a Signal Fragment.
Note: Boosts that increase the amount of rewards gained from PvE encounters will not increase the amount of dropped fragments.
Second Stage: Defeating the Boss Units
Once you've collected the required amount of Signal Fragments, a button labeled "Decipher Signal" will be active. You can tap that button whenever you like to initiate stage two of the event.
Tapping the button will present you with a list of boss units - the S-Collosus Mk5. The button next to each boss will take you to that boss' location on the World Map.
These bosses are special in that they can only be attacked by you. Allies can't join in to help you in these battles.
In the same manner, you might see other boss units on the World Map, that belong to other Commanders, but you will not be able to attack them. Bosses you can't attack are indicated by their grey border.
If you manage to defeat all of the bosses, then congratulations! You've successfully completed this event and can enjoy the rewards!
Note: All undefeated boss encounters will despawn when the event ends.
If you're in an Alliance, you can check the event progress of your alliance members in the Alliance Progress sub-menu of the event. In this menu, you'll be able to see how many Signal Fragments each member has collected and how many of their bosses they've managed to defeat.