More Info On German Customs Duty Label Needed

Hi all,

I found the following label in my accumulation (unfortunately, it is on a 'standalone' piece, having been removed from the original cover). I did a google translate search and understand that it is some kind of customs duty label, most likely used during the Third Reich era given that the currency used was RM as opposed to DM.

Would anybody be able to provide more details on the label, such as under what circumstances it was used, its period of usage, what the red marking meant etc?

Many thanks in advance!

The overprint on the label states that the contents are not subject to customs duty.