Growing up, my teachers always stressed that a mistake is a mistake and that with careful double checking, I should have caught those mistakes.
As a teacher, I realize that's simply not true.
There are lots of different reasons for mistakes, especially in math.
I love this anchor chart.
I would change the word silly to careless, but other than that, it's a wonderful way for students to think critically about their math errors. From there, they could engage in a more meaningful conference about what they need to work on: carelessness, math computation or processing.
I would hang this below a sign that says mistakes are proof that you are trying.