Fairly certain the first recycling symbol originated in Europe in the 1950s, which was known as the "Blue Stem", and it represents the recycling of paper and cardboard.  The symbol has since evolved to be adapted for other types of materials. In North America, recycling systems that use colored and/or bar coded labels are often referred to as "color codes". Plastic containers are sometimes labeled with a symbol such as this recycling symbol, and sometimes with identifying numbers or letters. Bar codes are often produced in blue and white colors, and are used to identify items for collection and/or recycling.  The recycling symbol is usually black and white, and is intended to be legible from a distance.
assistant
After the arrival of plastic containers in the 1950s, recycling much of plastic was encouraged because it was burned to produce fuel.  The recycling symbol shown here is denoted by the words "Recycle", a triangle made out of arrows, and a circle.  It contains the letters "HDPE", which stands for High-Density Polyethylene, a form of Polyethylene.  For North American recycling, containers are often labeled with a number system to indicate the type of material used in the product.  Different numbers are used for
assistant
Can you explain how the designations on plastic containers that allow them to be sorted and recycled?
user
Well, products in North America have bar codes that are used to identify them, as well as to help with organizing them into recycling bins.  Plastic containers are sometimes also labeled with product codes and/or numbers, along with the recycling symbol shown here.  TODO: Edit the existing text to include an explanation of other labeling systems.
assistant
Okay. Can you tell me about the numbers and symbols used for recycling plastic containers?
user