I've released on ELPA the new package kind-icon, which adds simple, lightweight text or monochrome icons to the prefix margin of compatible completion UI's, matching by default the font-lock colors of variables/functions/keywords/etc. Many backends like lsp-mode support the :company-kind completion property, which is how kind-icon determines the kind. Since text and icons all take up the space of precisely 3 characters, alignment is always pixel perfect.
kind-icon is easy to set up, and works either as a "margin-formatter" function (for supporting UI's such as the excellent [corfu] completion front-end), or by wrapping the completion function, for other completion UI's which can handle the Emacs 28+ affixation-function completion property.
An example of kind-icon in action with corfu:
kind-icon with corfu and orderless, in lsp-mode
And with more than 6500 icons instantly configurable by name, you can easily make it your own...
