It’s called a mnemonic device.
When I first started as a firefighter, I noticed that I would sometimes have trouble remembering what color fires were. Naturally, this proved to be quite troublesome. So I was forced to adapt. Eventually, I came up with a neat little memory trick based on the observation that a firetruck, much like fire itself, is red. So now, anytime I forget what a fire looks like, I simply remind myself that fires are the same color as firetrucks.
Of course, like all things, my mnemonic is not perfect. One major difficulty that I’ve run into is that fire is not the only thing that is red. Indeed, it turns out that stop signs, tomatoes, and many types of birds are also red, and yet none of these things are appropriate targets for my 100 foot long industrial strength high-pressure fire hose. So, how exactly do I distinguish between a cardinal and a giant blazing inferno? The answer is context.
When I see something that is red, I ask myself a series of questions about my surroundings. Do I hear a crackling sound? Does it smell like burning popcorn? Are there people in the vicinity running around and screaming, “Help, for the love of God, someone please put out the fire”? If the answer to any of these questions is yes, there’s a good chance that the red thing I am looking at might be a fire.
Now, I’m sure I would be just as good of a firefighter if firetrucks were blue. All I’m saying is, it’s a good thing firetrucks are red, because it makes my job a hell of a lot easier.