I've made a userscript to do this.

Update: This has been added to the dev version of [my SE Additional Optional Features userscript](http://stackapps.com/questions/6091/se-additional-optional-features) - please install that instead of this. Any updates will go straight to that userscript, not this!
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Get it at [Github](https://github.com/shu8/SE-Answers_scripts/raw/master/newMetaQuestionModAlert.user.js).

It gets the latest 5 questions posted on the per-site meta of the current site and adds a diamond to the topbar.

It is red if there are new questions, and white if there aren't.

It decides whether you've seen the questions by saving the latest question via `GM_setValue` - if the latest question via the API is equal to that, it will show white. So, basically once you click the button, it will go white the next time.

![enter image description here][1]

![enter image description here][2]

Note: I have no experience with the standard mod diamond so sorry if it doesn't look right!

On sites without a meta, it will always look like the bottom gif above.

V1.1:

- added support for multiple sites (I forgot about the possibility of using multiple sites last time!)
- made it so the box closes if you click outside it
- made it work in firefox (thanks @Brock :)

  [1]: https://i.sstatic.net/Y3XA0.gif
  [2]: https://i.sstatic.net/Dya3I.gif