This script adds a Winterbash hat-count to every user "Signature block" on questions, answers, review pages, etc. For example:

Reference this feature request: Show hat count in user card (next to badges).

This userscript requires an engine that supports both @require and GM_xmlhttpRequest. It was tested on Firefox + Greasemonkey and Chrome + Tampermonkey.

To install, click here (Hatoverflow.user.js install at Github).

To preview the source, click here (Hatoverflow.user.js preview at Github).

Notes and known issues:

1. (Update:) Added a check to turn the script "off" unless it's December or January, but I recommend that you uninstall or disable the script when Winter Bash is not in effect. This saves resources and is one less thing to bog down the server, or your browser, unnecessarily. (Not that the script is slow, but tiny things add up.)
2. No attempt is made to distinguish between users with no hats and users not participating in Winterbash.
3. Results are cached for up to 2 hours. This is to avoid hammering the API and tempting the API developers to hammer back. A two-hour update rate is more than fast enough for hat coveting. ;)
4. Uses the undocumented Winterbash API, so it's subject to change without notice.
5. In some cases, the badge display might get clipped on the right side. This is "won't fix", for now.
6. Only the standard, mostly static, signatures as found on: questions, answers, review pages, etc., are supported or modified.