So, after some short testing it seems, not only do flares have little effect unless they're hit very early (during the target is locking you) the only warning that is given is a small visual cue which, in most cases, doesn't really help if you're focused on flying when it happens.
Currently IRL, pretty much all modern aircraft, both fixed and rotary have Missile Warning Systems which create audible and visual cues, with many automatically firing flares upon detection of a missile lock.
Now i'm not saying a indepth and thorough system is needed, just an added audible cue for lock (a beeping tone), a separate one for launch (a faster paced or longer beeping/tone) with the option to allow automatic firing of flares.