https://creativecommons.org/publicdomain/zero/1.0/https://www.rawpixel.com/image/8800002
"I'm Clean" Bumper Stickers Are Given to Any Motorists Who Wish to Place Them on Their Vehicles after Passing an Inspection at an Auto Emission Inspection Station in Downtown Cincinnati, Ohio Since the Beginning of 1975.
All City Motorists Must Pass the Long Standing Safety Check Only Once a Year. An Emissions Test on an Exhaust Analyzer Has Been Added for All Light Duty, Spark Ignition Powered Motor Vehicles to Monitor Safe Levels of Carbon Monoxide and Hydrocarbons. 09/1975. Photographer: Eiler, Lyntha Scott. Original public domain image from Flickr
Public DomainFree CC0 image for Personal and Business use