If you have a Swedish registration number for the vehicle you can check here;
https://fu-regnr.transportstyrelsen.se/extweb/UppgifterAnnatFordon/Fordonsuppgifter
Under "Status" there is "Påställt första gången" and a date. That is the date when (for ex-military vehicles) they were first registered by the military (most often between 1975 and 1979).
Under "Sammanfattning" there is "Fordonsår" and that is as mentioned earlier in most cases 1975 for the TGB 11 (4x4) and TGB 13 (6x6). The TGB 20 (flatbed with back-to-back seats), from where your pictured sign originates, are in most cases manufactured later, say early to mid 1980's. It also has five forward gears as opposed to four on the TGB 11 and 13.
The sign in your picture is on a TGB 221, originally used by anti-aircraft platoons for transporting men and anti-aircraft missile launchers RB70 and later RB90. The back-to-back seats covers 2/3rds of the flatbed, the last 1/3rd is storage for the missile gadgets, accessible from the rear of the vehicle.
/pbv301