Cocked and locked? Probably safe.
But I agree with others: the Luger is a pretty old gun, and I'd like a more modern gun for self-defense.
You know: more rounds, easier to clear when you have a jam (and if my experience with Lugers is any indication, you'll have a few jams), and sights that actually help you "sight" the gun...
Great, fun gun, however, and mine is very accurate. (Despite the horrid sights.)
(Mine, fresh back from a trip to the gunsmith, and a new sear, went full auto at the range. Luckily I was using a crappy mag, and there were only 3 rounds that fired off.
That was an interesting experience. There was a little burr on the small piece that acts as a decocker on the side...)
One acquaintance, a very accomplished master-level IDPA shooter (4-gun master) once used a Luger to shoot the top time at a pretty well-attended IDPA match. The guns have some potential, in the right hands.