Oh yeah, I remember those.....they drove me in desparation to re-register my maroon 1967 car in Nevada to get out of it- the height of the foolishness was around 1974-1977 if I recall.
The NoX sticker meant the car HAD to have some retrofit smog aftermarket device, made by approved companies, installed on EVERY California registered car from 1966-1970 ( I think) whenever the car was registered or transferred, the light blue NoX sticker was affixed to the car upon transfer or registered.
I felt and still do, the whole thing was a scam by the companies who made the devices, there were 3 o4 4 companies that did, I think it involved plugging one of the vacuum lines and some other measure of dubious benefit which made the car run worse and get worse MPG.
I think the program died a quiet death, after a passage of some years and so few 1966-70 cars on the road it did not seem worth to continue enforcing.
It brings back awful memories. Like that of the CHP stopping every Nevada or Oregon plated car they saw to try and find and catch evaders like me, my story was, when pulled over in the Cougar, that I had a Calif D/L and a Nevada plated car was that I went to Reno to find a job, re registered the car there, couldn't find a job and moved back to Calif again, before I had a chance to get my D/L changed to Nevada.
These were the years the Feds mandated ever stricter smog/DOT laws, like
the very first catalytic converters, railroad tie car bumpers, all manner of engine mpg and power robbing restrictions, resulting in the 6 mpg 1973 Pontiac Grandville sedans, Joan Claybrook 85 mph speedometers, and cars that coughed and stumbled on their hands and knees to 60 mph, truly an awful time to be a car enthusiast, those were the awful old days...
The red NoX stickers were only given to cars with motors that the aftermarrket NoX systems couldn't be fitted to, like exotic carburetted versions of Maseratis, Mercedes and diesel passenger vehicles and the like.
To give an idea of what it must of been like, imagine having to retrofit one of these crappy devices to a 1966 GTO with a 389 and 3 deuces on it. Just disgusting.
Those decals were truly a mark of shame, the only thing they could possibly represent today is a "period correct" reminder of one of the most shameful examples of the Government meddling with innocent car owners' vehicles and telling them what to put on their cars.
Who on earth got hold of these stickers and is selling them anyway?
My goodness, you really got me going with this one.
Jim B.