That is the coolest drone I've seen.

That's a very cool design <3

As for mature, I'd think more than the hidden face, it would be the padlock sigil and its location that would require a mature tag.

I'd say the crotch lock kinda makes it inherently sexual so I'd say that it should be mature.

It's just a symbol on top of clothes (and its' clothed) so to me it seems like a detail that's up to the viewer to interpret what it means. I feel like a lot of art is this way where many details either are or are not sexual to people, when you're not into a thing it sparks no sexual thoughts or assumptions. But obscured faces could cause anxiety in some people (I'd rather there was a content warning function for this).

The OC is a faceless character. I don't see anything wrong with that. And the lock symbol is just that: a lock symbol. Any of this stunning art, in my opinion, should be labeled as Mature.

I'm thinking more mature because of the lock symbol and it's location. There's been a years-long string of artwork from multiple artists that turn the combination into what's called a "nullge" and still attempt sexual actions on it (which makes it adult due to context). I'd be safe here and throw it into mature.

I don't think it should matter what other artists have drawn and if other art had sexual actions going on, with the exception if this was published as a bundle with different art or with a story (then you'd label everything mature if just one image/part of story was so). But this is a stand alone upload and there are no sexual action going on this image, it's only viewers judgement what they want to imagine about it. The other exception would be if this was about some major scale political event affecting peoples lives, but it's not.

I was more concerned that hidden faces without an obvious mask/prop can cause anxiety (but I'm unsure if that's farfetched)

Nah. Hidden faces are nothing, especially when in superhero comics there is The Question.

Interesting, I hadn't come across that one even though I like superhero stuff. I kinda associated the blank face with stuff like slenderman (horror) and some recent local events where people put a stretchy hood on their face to not get caught in doing violance. Might actually be that my thoughts came from the recent events, because now that I think about it again, it seems silly (people do have all sorts of fears but surely it's not that common). And I guess spiderman is like that too, even if the mask does have obvious eyes.