So far all perks I’ve seen (that means almost all perks in offense category) shows its activation or effect in some way. You can definitely tell whether a perk is activated or in effect. For example, an additional text named “fast adaption” is shown during relevant situation. Similarly, you can also see the increment of damage enabled by perk Full Force. As for Berserk, there’s no noticeable indication when the effect is triggered, but it’s quite unlikely you wouldn’t notice the sudden restoration of AP.
So…… I’m not sure if Head Hunter is the only exception.
P.S.
On an irrelevant note, I kinda like the part where the game tells you if an effect is triggered. Most games miss out on this tiny feature.
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