Here we go again
If you are employed as first officer/co-pilot;
If you are only RHS qualified;
You can log PIC time only when your P1 is incapacitated.
However, you can log P1/US or PiCUS if you don't have 250 hr PiC required to unfreeze the ATPL. Whether logbook entry has to be countersigned, depends on your company or local CAA.
And if your local CAA is incompetent/understaffed/not caring you can log anything and get away with it. There might be some problems when you're switching employers, though.