Strange key removal warning

This morning, I went to go start up the car and found that it had a dead battery. Thought I would give it a jump and it would be fine, but now when I turn the car all the way off and step outside, there is a warning. One beep inside the car, three beeps outside, and a yellow light with a key and an exclamation mark.

It almost is as if I am trying to leave the car with it on, but the dashboard lights, etc. are off. The fob doesn't work to lock or unlock the car.

I reset the computer by unhooking the 1 volt for a few minutes, and the fob worked until I started the car for the first time - then we were back to the same warning tone/light behavior.

There was a brief warning after the first jump and the reset about the parking system "P lock malfunction - engage the parking brake and park on a flat surface, etc", but it wasn't persistent (and from what I can tell is expected behavior when the computer reboots). I also never figured out why the battery went dead, and am thinking that what I'm seeing now might have actually contributed (like it something wasn't turning off all of the way, or if it was in some sort of warning cycle loop for the two days it was parked).

Any ideas?