Requested feature overview description.
A text-shadow around the up or down arrow to indicate your current vote on a comment.

For example, text-shadow:0px 0px 5px #FF0; for the green arrow or text-shadow:0px 0px 5px #FFF; for the red arrow (adjust as needed).

Why would it be useful?
Prevent accidental unvoting, let user remember their vote.

What part(s) of the site page(s) are affected?
Comments index, comment search, posts.

Augh, I knew I forgot something when implementing that. I think I'll make it match the way posts are voted, where the arrow is the right color only when that is the current choice. Just to keep things consistent.

I made some css changes on those arrows for myself. May take or adjust it if you like.
Screenshot: http://i.imgur.com/lauax7E.png

a {
background-color: rgba(255,255,255,0.2);
border-radius: 3px;
padding: 0px 7px;
}
 
a:hover {
background-color: rgba(255,255,255,0.05);
}
 
a:active {
background-color: rgba(255,255,255,0.2);
}
 
a.greentext {
background-color: #3e9e49;
color: #fff !important;
}
 
a.redtext {
background-color: #e45f5f;
color: #fff !important;
}

The "hitbox" for clicking on the arrows is very small. ZaSigma4's change may make it a lot easier to click.

Implementation created. Need to profile it to make sure it isn't going to make comments take significantly longer to load.

I left the styling alone for right now to keep it consistent, but will look into some potential ways of making it easier to use accurately.

This did not make it into 1.1.2 because it had not been tested enough. I hope to deploy this in a follow up in the next week or so, given the time.

At long last this made it out in 1.1.3.1 on 2016-11-26.

Bumping with style changes:

span[id*='comment-vote-up'], span[id*='comment-vote-down'] {padding: 0px 5px 0px 5px;}
span[id*='comment-vote-up'] a, span[id*='comment-vote-down'] a {visibility: hidden !important; position: relative !important;}
span[id*='comment-vote-up'] a:after {visibility: visible; position: absolute; left: -4px; content:'\0025B2';}
span[id*='comment-vote-down'] a:after {visibility: visible; position: absolute; left: -2px; content:'\0025BC';}
span[id*='comment-vote-up']:hover a:after {background-color: rgba(255,255,255,0.2); border-radius: 3px;}
span[id*='comment-vote-down']:hover a:after {background-color: rgba(255,255,255,0.2); border-radius: 3px;}

// ==UserScript==
// @name        Comment Voting
// @namespace   Lance_Armstrong
// @include     /https?://(e621|e926)\\.net/post/show/.*/
// @include     /https?://(e621|e926)\\.net/comment.*/
// @grant       GM_addStyle
// ==/UserScript==

GM_addStyle("span[id*='comment-vote-up'], span[id*='comment-vote-down'] {padding: 0px 5px 0px 5px;}");
GM_addStyle("span[id*='comment-vote-up'] a, span[id*='comment-vote-down'] a {visibility: hidden !important; position: relative !important;}");
GM_addStyle("span[id*='comment-vote-up'] a:after {visibility: visible; position: absolute; left: -4px; content:'\\\0025B2';}");
GM_addStyle("span[id*='comment-vote-down'] a:after {visibility: visible; position: absolute; left: -2px; content:'\\\0025BC';}");
GM_addStyle("span[id*='comment-vote-up']:hover a:after {background-color: rgba(255,255,255,0.2); border-radius: 3px;}");
GM_addStyle("span[id*='comment-vote-down']:hover a:after {background-color: rgba(255,255,255,0.2); border-radius: 3px;}");

It'd be nice if thumbnails had an indicator for you upvoting/downvoting the post. Like if the thumbnail score was highlighted a different colour depending on your vote or something like that.

JAKXXX3 said:
It'd be nice if thumbnails had an indicator for you upvoting/downvoting the post. Like if the thumbnail score was highlighted a different colour depending on your vote or something like that.

This is about comments, not the post index.

The way I handle post voting is by adding -voted:username to my searches, and then pasting them on my profile. That way I don't see them again.

Example: anthro order:score date:yesterday -voted:JAKXXX3

Been a user here for nearly a year, yet I am finally noticing this indicator. I feel dumb.