Mortar security with a piece of tape

Have you seen fireworks mortars with a piece of tape in it's mouth like in the picture below?

There is a simple reason for that: security!

With a piece of tape in the mouth of the mortar, pyrotechnics can check if it is loaded or not. For example, think about the end of a fireworks show, pyrotechnicians have to collect the fired mortars and sometimes there are misfires (shells that have not leave the mortar for some reason), so this is an easy way to check it, because if the tape is broken of flown away it means the shell has also leave the mortar.