Why am I seeing this?

Sounds a lot like filesystem corruption to me. It happens (although rarely). Could be an early sign of disk failure too. Time will tell in that case.

Make sure you have a recent backup, and then run Disk Utility and do a repair on permissions first, then on disk. (The latter will require you to boot from Recovery Partition, or from the OS X Install DVD.)

 

Looks like a busted system font to me....

 

This. If you have been mucking with fonts this is often the result. Some software you installed could have clobbered a font as well.

Do some searching on OS X and fonts, you will find something. I personally haven't come across this since 10.5.

 

This is almost definitely a system font problem.

Can you make a new user account and see if the problem persists (you could narrow it down to your own user Library this way), and if it does then it's a problem with the font in the main global Library.

The other thing is to check your localisation settings - something might have gone awry here.

Did you use any software that claims to help you recover space on your hard drive that removes installed printers/extra languages etc? You might have deleted a system font you were relying on due to a setting that the software might not expect a typical user to be using. (UK English vs US English, for example)

 

How do you spawn the popup? Does it popup by itself without interaction, or are you clicking something?
Does the mentioned issue affect only that popup, or also other popups/menus/windows system wide?
What are you doing in order to bring back the normal font?

 

Your issue is probably due to the font cache. Assuming you have an OS that ranges between 10.6 and 10.8, here are the steps you should take:
- close all your apps
- open the Finder, browse in applications and find the folder named Utilities: open Terminal
- paste this string

Code:

sudo atsutil databases -remove

Hit enter.
You will be asked to insert your admin password. Type it, and hit enter again.
Restart your computer.

 

I cant imagine any benefit to be gained by that gift of fonts to you, I would be wary of any similar offer in future.

 

"IF" it's disk failure, the Pros are very easy to swap out the hard drive, and restore from Time Machine.

 

If you suspect font caches are causing problems, you can clean them out with a small and free utility called "Yasu".
http://yasuapp.net

Just open it, and you will see the options to
- Clear system font cache
- Clear local font cache
- Clear user font cache

Put checkmarks in them, click ok, enter password when required, set the "when finished" popup to either "Restart" or "Shutdown", and let it go to work.

BTW, Yasu is very handy for running all the routine system maintenance tasks at once.