You called
TIR was just about dead by 1975, as there were simpler arrangements for EEC and EFTA (European Free Trade Association - a bit like a bigger EEC) countries, but had started in 1949.
Whilst not using the TIR arrangement, the TIR plate had to be covered up (god alone knows why) usually with a diagonal metal strap, which could be sealed in place by customs, using a lead seal and it looks like the Douanier is using his sealing pliers
How sad that I know that