On https://github.com/IntelRealSense/librealsense/blame/57e623cd7d5f3912ffae5af86e104d93577fedb0/doc/distribution_linux.md#L17 it recommends

sudo apt-key adv --keyserver keys.gnupg.net --recv-key 6F3EFCDE

short PGP keys are trivial to forge (32-bit integers), so it would be better if you could use the long PGP ID instead in the instrall instructions.