I like the idea of making it easier to understand mathematical notation, and get more practice at it. However, using flash cards to implement it could be problematic.

As I learned more and more mathematical notation while studying engineering, it became clear that a lot of the interpretation of the notation depends upon context. For example, if you see vertical lines to either side of an expression, does that mean absolute value or the determinant of a matrix? Is i representing the imaginary number, or current, or the vectors in the same direction as the x-axis? (As an example, electrical engineers use j for the imaginary number, since I represents current.)

For a sufficiently narrow topic, the flashcards might be useful, but it might set up false expectations that the meaning of the symbols will apply outside that narrow topic. There is not a one-to-one correspondence between symbols and meaning.