From 1968-1971, collectors 'Buttons' (aka 'Badges') were packaged with the Hot Wheels vehicle. They were either metal or plastic and featured an illustration of the vehicle. Vehicles sold in Canada in 1972 had a plastic button with an illustration of a Mag Wheel instead of the individual vehicle.
Metal buttons were produced from 1968 to 1971 and had a long tab extending from the edge of the button which could be folded over to attach it to something, the tabs could be found with either a smooth or 'notched' end. Metal buttons were produced in Hong Kong or the USA which was printed on the lower edge of the button.
Plastic buttons were produced from 1970-1972 and had the tab cast into the back side of the button. They were also manufactured in both Hong Kong and USA, but this is usually ignored by collectors.
This page is for my personal collection of Redline Buttons, and does not cover all variations as there are some which I do not believe are significant enough to add to my collection. Please see RedlineButtons for a complete guide.