rothnh called it.
I have about 20 Autographs, mostly from the pre-filter vulcanite era. I think they started using acrylic sometime in the 1990s. Several of the vulcanite stems have the logo completely worn/buffed away and several more have logos that are VERY faint. All have black stems (even the acrylic ones).
I have never seen an Autograph with an acrylic stem that had the logo worn away. Autographs nearly always have a very distinctive scultured look to the stem. The style varied over the years and, I suspect, from one carver to another but the look is unmistakable.
Here's a good example of what to avoid:
http://www.ebay.com/itm/LIGHTLY-USED-SAVINELLI-AUTOGRAPH-SAND-BLAST-PIPE-140-/161011719293?pt=LH_DefaultDomain_0&hash=item257d0bdc7d
The stem is a replacement and not a very good replacement. The seller refers to the value of a 000 grade Autograph, implying that this grade 5 might be worth as much.
There are a lot of nice Autograph 4s & 5s in the $75 to $100 price range, take the time to look carefully and you can find a real treasure.