Makes the Google docs share button red when only the author has access. To install click the `Raw` button and your userscript extension will take it from there.

docs_red_when_unshared.user.js

// ==UserScript==
// @name         Red Share button when only I can see the file
// @namespace    http://bigethan.com/
// @version      0.1
// @description  To prevent sharing unshared docs, this turns the share button on google docs red when it's only shared with me.
// @author       Bigethan
// @match        https://docs.google.com/document/*
// @grant        none
// ==/UserScript==
(function(document) {
    'use strict';
    setInterval(function() {
        let button = document.querySelector("#docs-titlebar-share-client-button > div");
        if (button.getAttribute('aria-label') == 'Share. Private to only me. ') {
            button.style.background = 'rgb(232, 74, 26)'
        } else {
            button.style.background = 'rgb(26, 115, 232)'
        }
    }, 5000);
})(document);