Ever since Taffe’s introduction, her eyes have always had the slightest glow to them. Much later, we discover that she’s actively using her power all the time because she’s deaf, and she amplifies sound to help her hear.
There's also another small hint to this - Taffe is Brutally Honest, and that is an actual trait of deaf people.
When Muneca told her platoon and Kathy Lee about Hermes, Cinna guessed that his codename might be Mercury. Mercury is the Roman name for the Greek Hermes. Keep in mind that Cinna is from Italy (home to the Roman Empire); she would’ve grown up hearing about the mythologies with the Roman names, as opposed to the Greek versions that the others likely would’ve heard.
Why are the Torbern sisters so protective of each other? We know from Word of God that their parents died in a war. It's likely that they are the only living family they've got left - so naturally, they don't want to lose each other.
Larima uses her power quite a bit (she's something of a show-off). It makes one wonder if she's doing it on purpose, so she won't have to live too long without her little sister Taffe when Taffe almost inevitably dies before she does.
Observe Muneca's wince when Qamra reveals her eyepatch to the others. Why did she do this? Because Qamra lost her eye and ear to a fire attack. Muneca knows all too well what it feels like, since she was burned in a fire as a small girl, and has extensive burn scars which still hurt to this day.
We all know that Daryl Smithson inherited her power from her grandmother Helen Churchill, right? Helen was a very famous (and powerful) Pacificator of Light - so renowned, indeed, that decades later, people are expecting great things out of Daryl (when they find out who her grandmother is). We also know that Daryl discovered, on her own, how to use The Power of the Sun, and we later find out that Helen had tried to teach Daryl how to use this power (but was stopped from doing so). So, Daryl is obviously a Legacy Character where her grandmother is concerned...
...and yet there's more. The power of Light isn't just restricted to the visible light waves - according to Word of God and the "Building Up The World" series, the so-called power of Light is actually the ability to manipulate the entire electromagnetic spectrum, from radio to gamma waves. But the vast majority of Light users couldn't push beyond the visible colors (as confirmed by the fact that Daryl was the first person to discover how to use microwave waves to sting people). CastellaBrandsford abused this ability to kill thousands of people by radiation poisoning.
We also know that Castella was considered one of the best Pacificators of Light ever, up there with Helen. In other words, Castella had the exactly same abilities Helen has.
Now, let that sink in: Daryl has access to the exactly same kind of power that Castella did. This is why Daryl's mother was so freaked upon catching Helen training Daryl. Her mother was afraid Daryl would end up like Castella - and the top-shots in the Pacificators are afraid of this, too. That's why they intentionally ranked Daryl as a "feebler" and tried their best to pull Daryl away from the combative platoons... if it wasn't for Bismun.
Furthermore, we now know for sure that having powers do indeed affect one's mental and physical well-being. Castella, after all, was infamous for her Sanity Slippage. Sadly, this means Daryl is at a real and legitimate risk of going insane.
and she amplifies sound