Based on input received from actual Route 66 travelers in 2010, the ratings are indicated by the traffic lights below and are subject to change. No state has signed every turn, so refer to a guide book before you make your next turn.
STATE ROUTE 66 SIGNAGE RATINGS
States that need improvement
States with Fair Signage, but getting better
States with good Signage
"Texas is all over the place. It probably got hit by sign thieves in spots. At last check, Texas is a hold-out on joining the National Scenic Byways program." Route 66 News
Illinois is missing a lot of signs and a guidebook (or GPS) is essential here.
Missouri has many missing signs and is taking years to replace them. In addition, their strict regulations prohibit Route businesses to have even a small directional sign!
"Oklahoma is pretty decent, but it tends to not sign the really, really old alignments. There may be good reasons for that, such as it going through residential areas, plus the pavement is a fragile in spots. It may be best for only hardcore roadies to know about those.
New Mexico is iffy. So is California."
Route 66 News
In terms of signage, Missouri has recently made a huge improvement with the installation of of over 700 new "Historic Byways" signs, but some have already been stolen while other critical turns were overlooked.
Kansas and Arizona are also better than average but sign thefts are becoming a problem there as well.