But you couldn't rip the copy protection signal (not that you needed to, it was a fixed 4 letter string, "SCEA", "SCEI", or "SCEE" depending on region)

Nor could you burn it onto a CD-R. It was there to prevent people from burning copies of games, not to prevent you from ripping the disc.

Of course, it was stupidly easy to bypass with a mod chip. They literally just sit there injecting the copy protection signal into the cd rom electronics, tricking it into thinking every single disc was blessed by Sony, burned or not.