In the episode titled The End, (the very first episode of Red Dwarf) Lister goes into his room and feeds his pet cat, as he asks for the door to close a bare hand can clearly be seen outside of the spaceship window.
"Piers writes:
Yeah well he said out side the window not near the door !! "
not the point, the window is near the door, and to push the door back into place, a crewmember must be outside the window, as that is how the set is built.
In "continuity" though, we can theorise that whatever appears outside the window is space junk, as Red Dwarf has not left tho solar system yet, it could be a glove, or the hand of an astronaut who got a hole in his suit, caught in the solar panel, whicj is outside the sleeping quarters, as referenced in S1E06: "Confidence and Paranoia"