I don't know how to describe this item in English, but here are the images I prepared for it:

I initially wanted to make a glowing version (much like other forehead items) but I figured the black version also looks nice without a glow. I stylised it this way so that it's obvious that it's not an eye edit, but a tattoo. :)
Older files
Old CI:
I really like it n_n I don't think the item image can use pure black like that though, even if the wear does. I believe you need a little shading there, but I could be wrong C:
What does this look like with eyes and hair and stuff?
Thank you very much for saying so!
Thank you for the feedback! I had a feeling I was forgetting something. It's been years since I last drew CWs. :o
I did a few edits to the CI: 
Here are a few previews of the tattoo version and the mark version:



I thought of making the glow more diffuse, but it looks too messy when layered over hair.
how about a tiny glow circle behind it? So the black will suit black hairs too. I can show you in a min what i mean :)
I think I got what you meant. The glow can't be black, though -- maybe a light gray might work?

i would recommend doing a white and making it super transparent :D

i cant edit the layer bc im using an online program but i mean like a circle under it - not around the edges.
just turn down the opacity super low
either way you wanna do it is fine bc that looks good too just a suggestion <3
im SUPER new to cws so im not a great suggester myself lmao
Woops, I misread "glow circle" as "glow encircling". xD I think your suggestion might work too!
Here's what I tried, let me know if it's not exactly what you had in mind, though:

50% transparency - - 25% transparency