This falls under the following categories:
Where have I been all of my life?
You learn something new every day.
My son came home from school last week and asked me if I knew what the plastic tabs on loaves of bread meant. My response was, "yes, they are printed with the sell by dates." Little did I know they are color-coded by delivery date as well.
Snopes.com verified this newly-realized semiotic information for the plastic tabs and the twist ties.
According to Snopes, bread is delivered fresh five days a week to grocery stores: Monday, Tuesday, Thursday, Friday and Saturday. Each day has its own colored twist tie or plastic tab. This color-coding is alphabetical based on the first letter of the color which is coordinated with the order of the days of the week.
Monday - Blue
Tuesday - Green
Thursday - Red
Friday - White
Saturday - Yellow
The main purpose of the color-coding is to help grocery-stocking personnel switchover the bread inventory in a more expedient manner.
Now that I have this new information, I will never purchase a loaf of bread with a blue tab or tie on a Saturday.
From a previous post: semiotics is the scientific study of signs and their linguistic meaning. It is about the relationship between a sign and what it represents. It is about how people determine the meaning of signs. In semiotics a sign is considered anything (a symbol, an icon, a sound, a picture and so on) that stands for another thing.
More on semiotics here.