There are three places to find the correct inflation pressures for your tires. The owner's manual, The tire placard, Or the trailer's certification label which is located on the LH forward external section of the trailer.
The inflation pressure on the tire sidewall is the amount of inflation pressure need for the tire to provide it's maximum load capacity. For ST tires it's normally going to be the same figure that is found on the three locations above, but, that's up to the vehicle manufacture, because they are solely responsible for setting all recommended tire inflation pressures which are the correct minimum pressures appropriate for your vehicle.
USN - RET
DOD - RET
SSA - RET