Although not a model railway product, if you are one of our customers this is worth having.
We recently sat at home one evening and we got a notification on our camera to say someone was in the front garden, when we looked, someone had run in and taken two bin bags out of the bin and ran off down the street with them! We looked outside and in a quiet part of the street, loads of bin bags from different houses had been opened, someone was obviously looking for peoples names and addresses, or bank details etc.
This stamps a thick black ink over anything you want to hide so it can safely go in the bin.