System Settings icon
The system settings icon looks too much like an on/off switch. Something with either a gear or a wrench, as it is conventionally represented, would be a lot more intuitive.
Actually, I think our icon implements a widely-used and established metaphor for settings. It looks like the switches you'll find in the system settings.
Anyway, I'm open to discussion. While we are at it - we've got quite a few icons designs involving switches, cogs or physical representation. Maybe it's not always a plausibe representation for the app in question
Perhaps more than one switch would make it more obvious ? It's the single switch that makes it look like an on-off switch, especially when it's on the launcher. See the last icon on the launcher, for instance.

@pgera Just a small question, why aren't using Numix Circle and you're using Numix base instead?
@bil-elmoussaoui Just a matter of taste. I prefer the base icons over the circle ones. I find the circle icons to be over-simplified to the point that they convey less information.
In this case it's an issue for https://github.com/numixproject/numix-icon-theme. Since Numix is designed to be used combined with Numix Circle/Square the icon in question (it's the lowermost in your screenshot, light?) usually won't be picked for system settings.
That's where I had opened it originally. https://github.com/numixproject/numix-icon-theme/issues/1179
@pgera Sorry about that! I thought that you meant the Circle/Square icon. Can you please reopen the other one instead of this issue ? Thank you
Closing because using just Numix base is an unsupported use case.