"an inscribed or painted symbol considered to have magical power"
"a sign or symbol"
"... they are symbols that represent an intent, powered by activation (either from the sigil or just keeping its meaning in the back of your mind) and are used to tilt luck/the universe in your favor"
You can create your own or search the net for one you need (a friend sent me this one). There are also different ways to activate your sigil too.
What you give power to becomes empowered.