I'm an FO on a 74. I sign the flight release as PIC if I'm the more senior one on the flight deck when el jefe takes a nap (per company policy). Obviously, I'm PIC rated and take Captain PC's because our FSDO and company are a little backwards ("all our FO's are cruise captains!" Ridiculous). Nevertheless, I have never logged any of that as PIC in my logbook although I guess technically I could. It just seemed a little shady to try and pad my TPIC time and I would look at something like that with a hairy eyeball if I were doing the hiring. But, this thread probably had nothing to do with FOs.

Time asleep might be able to be logged as flight time. I spoke with an astronaut once and they said they logged the entire time they were on the mission as flight time (liftoff from Kennedy to landing at Kennedy or Edwards). Time was logged regardless of whether they were flying, scrubbing toilets, doing spacewalks or sleeping.

FOs don't sign releases unless your country of flying is different
First time I heard that anyway ....

Common in many parts of the world.

Common of First Officers to sign dispatch release as pilot in command ?

No... F/Os do not sign the release as PIC. However you stated,

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