This isn't really a mod, it's just a file I edited for my game.
For me, the default icons of Map Marker Overhaul (any of them) have two issues:
So I grabbed my favorite icons - the vanilla borderless style icons - and fixed those issues.
I added the missing states, and instead of tagging the icons with small letters, I changed their color. For icons with different states depending on tags - dungeon icons like forts, Ayleid ruins, caves and camps - the default color is slightly greyed out. Entered - meant to be used with the tags strong enemy, too hard lock etc - will turn red. Once the dungeon is cleared, the color will turn to match the other, normal icons.
I also changed three of the custom map markers you can set. It's now a flag for general points of interest, a tower (I use them for Maskar's outposts), a merchant bag (I wanted to use it to mark if I have to drop loot somewhere) and the old Ayleid ruin icon. I'm not super happy with the latter, but I don't really have any better ideas atm anyway.
All credits for the original icons go to xythen for the borderless map icons and theNiceOne for Map Marker Overhaul.