It looks like armor related to shar with all the dark circles...
so why does she make a secret of following shar. Its probably anyones first guess. The tattoos make it even more clear.
As followers of Shar are obsessed with being secretive its like an american spy boasting a big CIA tattoo
I think this is a metagaming area.
Larian might need to add religion check when you meet her, where based on armor you may determine she's a Shar follower, but it's also not beyond disbelief that your bloke of a character does not catch up on that or simply does not even know Shar symbolic proper, after all it's not like you have these things plastered all over walls in Baldur's Gate being common knowledge. Heck our 8 INT/8 WIS might not even catch all on that at all ever, let alone from taking a glance at armor after crashing from bloody spaceship and be like "yeah that's Shar cultist".
As for secrecy,
seems like Shadowheart was where she was not by sheer coincidence, the Gith were after her, the tentaclebois were just a bonus. Might explain Shar heraldic armor and such as part of circumstances.
I think from responses, as a whole, people assume here that everyone is well versed in detecting Shar cultists and in their tattoos and symbols - I assure you, it's not that simple. You have whole druid grove essentially duped and fooled by
Shadow Druids who literally were in front of their noses
and they did not even pick on
that, but they should be professional Shar detectors? lol
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That said, it could be pretty good if Larian would add some poncho or something over that armor when you meet her, she'd probably indeed be a bit more wary of being revealed and could have snagged some rag on the way from all these corpses that litter the beach to wrap above armor.