North Korea's registrations begin with P. As mentioned by Pat206, PT is a Brazilian registration (along with PP, PR, and PU).
The actual allocation to DPRK (N.Korea) per the ITU/ICAO list is P5- thru P9- however the aircraft are painted as P-nnn where nnn is between 500 and 999.
One of 5 countries which (presumably) have special dispensation to ignore the 'rules':
Canada - CF,CG,CH,CI,CJ and CK - displayed as C-xxxx
Zimbabwe - Z2 - displayed as Z-Wxx and Z-Yxx
USA N- but the dash is omitted
Japan JA- but the dash is omitted.
Most countries have additional allocations
which in theory could be used for registrations as happened recently in the UK where the M-xxxx was added to the G-xxxx series.