Okay, I'll bite.

[baxil]

http://img147.imageshack.us/img147/9924/donotpostbf3.jpg: A sign reading

DO NOT POST PICTURES OF THIS SIGN ON THE INTERNET
986F 64B9 3005 E03E FC42 A41E BD57 3179

Google doesn't seem to turn up anything relevant, but here's a Reddit thread speculating on its meaning (and whether it's Photoshopped; weak consensus there is yes).

Among the more interesting tidbits pointed out there:

• The hexadecimal code is 128 bits, which (among other things) is the right size for an MD5 hash.
  
• The user who posted the link to Reddit, "agent_langley" (Langley, VA being the home of the CIA), has posted only that single link so far (and two possibly unrelated comments to other threads).
  
• Converting it to eight Unicode characters gets three Japanese glyphs Han unified ideographs [See comments -B] followed by several other random characters from non-Asian languages.
  
• Converting to ASCII gets basically gibberish.
  
• It's not the AACS HD-DVD decryption key, which began with 09F9.

I wouldn't be surprised if it's some viral campaign that hasn't quite hit the denouement stage yet, but it's still an interesting brainteaser.

Edited to add: Well, that was quick. Apparently solved (less than an hour later!) in comments.