Yeah in a typical mutant detection campaign its a really bad idea to be discovered as a mutant but it takes special gear, which is a push -- and then there is the "not distinctive in some cultures" has to play in as well; not only will some people simply won't care if you're a mutant but mutants won't care. To me that looks like:
Mutant: Distinctive Features (Not Concealable; Always Noticed and Causes Major Reaction; Detectable Only By Technology Or Major Effort; Not Distinctive In Some Cultures)
And that's 5 points.
I mean obviously Nightcrawler's complication is different than, say, Marvel Girl's but that's the baseline.
That section "not concealable" is the key in this discussion; can you buy a device or take a power to cover up a distinctive feature that cannot be concealed? Sadly um, the rules don't actually say. No, seriously that huge two volume set doesn't actually say what makes a distinctive feature "unconcealable" or how that prohibits the use of things to hide it.
It sounds odd to say that Mutants cannot conceal their mutanthood but that's covered by the detectable only by tech or major effort. Basically that means (to me at least) that its only possible to detect being a mutant in this complication with a device, but if you have that device you cannot hide your status from it.
To some degree we can figure it out: this is a feature so distinct and obvious that even a disguise won't hide it. The Thing, for example. Having a gigantic pair of wings on your back (although Angel folds them away pretty amazingly well!). Spock can hide his ears under a hat or a cheesy 80s headband. A dwarf cannot hide how short they are without some extraordinary effort and device (two dwarves in a trench coat). Groot cannot hide that he's a tree even with Ben Grimm's fedora and overcoat. But its not even touched on in the rules, its just referred to.
And obviously a power purchased to conceal something will, even if it cannot ordinarily be concealed. Invisibility can make a really distinct glowing amazing thing not visible (Ben Grimm being made so by Invisible Girl). Images can conceal a dragon, despite being 60 feet long and made of scales.