When you follow a link to a comment or answer you might end-up being confused if the answer or comment is removed. 

This little userscript shows a warning on top of the page when the link you just used contains a fragment to an answer or comment that no longer exists on the page.

    // ==UserScript==
    // @name         Check if comment and answer exist
    // @namespace    http://meta.stackexchange.com/users/158100/rene
    // @version      0.1
    // @description  Show a message if the answer or comment in the hash of the url doesn't exist
    // @author       rene
    // @match        *://*.stackexchange.com/questions/*
    // @match        *://stackoverflow.com/questions/*
    // @match        *://serverfault.com/questions/*
    // @match        *://askubuntu.com/questions/*
    // @match        *://mathoverflow.net/questions/*
    // @match        *://stackapps.com/questions/*
    // @match        *://superuser.com/questions/*
    // @grant        none
    // ==/UserScript==
    
    (function ($, window) {
    
        var hash = $(window.location).attr('hash'),
            msg = $('<div></div>')
                        .css('background-color','#CCFFCC')
                        .css('align','center')
                        .css('padding', '10px')
                        .css('text-align', 'center')
                        .hide();
    
        function showMessage(jqsel, text) {
            if (jqsel.length === 0) {
                $('div#header').append(
                    msg
                    .text('The ' + text + ' is not found. It may have been deleted')
                    .fadeIn(2000)
                    .fadeOut(5000));
            }
        }
    
        if (hash.length > 0) {
            cleanHash = hash.substring(1);
            if (cleanHash.indexOf('comment') === 0) {
                ids = cleanHash.substring(7).split('_');
                showMessage($('div#comments-' + ids[1]).find('tr#comment-'+ ids[0]), 'comment');
            } else {
                if (Number.parseInt(cleanHash, 10) !== NaN) {
                    showMessage($('div#answer-' + cleanHash), 'answer');
                }
            }
        }
    }($ || unsafeWindow.$, window || unsafeWindow ));

You can find it ready to be consumed by TamperMonkey or GreaseMonkey on the [Github repository](https://github.com/rschrieken/SmallButHandy/raw/master/CheckForExistingCorA.user.js). 

If you find a bug or have a feature request either create an [issue](https://github.com/rschrieken/SmallButHandy/issues) or leave a comment here.

Allow for 6 to 8 weeks before fixing. 

Here is an [Animated GIF to show the script in action][1]

*This is a repost of [my original answer](https://meta.stackexchange.com/a/251236/158100) on Meta Stack Exchange*


  [1]: https://i.sstatic.net/XNpge.gif