Our department received a letter from our dispatch center about this. I have spoken with the director of the dispatch center and he is supposed to email me a link to a FEMA page that address' this issue.
I personally believe it to be some type of "urban legend" that someone is trying to get going (who know's why). Of course having used the current system we use for over 15 years, and knowing over 70% of the homes in our area have scanner systems, this takes away ALL ability to maintain some security. While i know most people with scanners know the codes, most of the people the police deal with don't and it raises a level of intensity when a dispatcher comes across the radio and say's "that subject has a felony warrant," instead of "the subject has a 10-17 F (our code for felony warrant).
I am still researching this, and as soon as i do find something, i'll post it here for others.