The positive and negative electrodes are marked on the battery package. If you are afraid of insecurity, you can get a polar LED.

Next, the pin will light up only when it is correctly connected to the positive and negative poles.

Polarity judgment of light-emitting diodes

The longer of the two leads of the LED is the positive electrode, which should be connected to the positive electrode of the power supply. Some light-emitting diodes have the same length of two leads, but there is a raised uvula on the shell, and the lead near the uvula is the positive electrode.