I am looking at buying an M16 and have heard some nasty rumors about getting the local CLEO to sign off!?
 Anyone gone through this in Marion or had any problems?
Any info would be greatly appreciated.

I've done two Form 4s and a Form 1 in Marion Co.

Take your shiz down to Citizens Services in the City-County Building (same place you go for your gun permit apps) and explain to the clerk what you have and what you need. They'll have you fill out a background check request and an IPD fingerprint card (in addition to the two from BATFE, that you should have with you), then they'll take $9.00 from you and do three sets of prints (one for internal use, the other two for BATFE). You'll get the ATF cards back, and the IPD card will be sent down along with your forms for processing. Go home. In a week or two, you'll get a call from the Citizens Services folks saying your forms are ready; you can either pick them up, or direct IPD to mail them to you.

Takes a bit of time, but all of mine got approved like clockwork. Drop me a line if you have more specific questions.

Much appreciated thanks for the  Info
 I hate to say this but that post count is kinda scary.

This was several years ago, so it may not be much help. In 1996, I think, I had one done when I lived there, and bought an integrally suppressed gun.
I was in the Marion Co. Sheriff's Dept jurisdiction, so went through their office for the sign off, but through IPD for prints. Whatever- it was my first Class 3, and I just followed the dealer's instructions.
I went in, found the Sheriff's secretary, and told her my business. She said something to the effect of- "Fine. Leave it in the inbox".  
I figured that was that, and I'd never see those forms again. I thought if I was lucky, maybe I would get it after some phone calls and return visits.

I think that was a Friday, but maybe a Thursday.  Anyway, it came in Monday's mail! Not only did I not have to beg for it, but it was sent ASAP by them.
 

Colts is exactly right.  It takes awhile, but they still do it.  Get it down there.  You'll get it signed.  I just did mine back in march.  Although I wound up not using it after I fast tracked it.  (Its all about who you know)  

My last Form 4 (June 2004) took 2 weeks to get back, I picked it up, but it did get signed.