Display a character as the colorcolumn.

Use your favourite plugin manager to install.

wbthomason/packer.nvim

-- init.lua
require("packer").startup(
    function()
        use "lukas-reineke/virt-column.nvim"
    end
)

junegunn/vim-plug

" init.vim
call plug#begin('~/.vim/plugged')
Plug 'lukas-reineke/virt-column.nvim'
call plug#end()

To configure virt-column.nvim you need to run the setup function.

require("virt-column").setup()

Please see :help virt-column.txtfor more details and all possible values.

Thank you @francium for the idea.