Who wrote “Don't Open, Dead” on the doors inside in the hospital?

Question

Who wrote "Don't Open, Dead Inside" on the doors in the hospital that Rick sees after waking? Do they ever show it?

Answer 1

It was never shown in the comics, upon which the series was based. The words were written there presumably before the hospital was abandoned, possibly after a large number of patients had been moved into that one area (to better concentrate care) and one or more passed, raising as walkers, and began turning the others.

The person who wrote it was warning others that there were no more living patients past that point. They presumably left the hospital when it was abandoned by the living (or were killed there, when it was overrun by the dead).

Answer 2

The military could have been keeping them in there prior to shooting them. There are bodies lined up outside the hospital and evidence that the military was there. It seems like the military was shooting the walkers and placing the bodies there. It's right after Rick uses the matches to find his way out of the hospital using a stairwell. Also, in a later episode it shows how Shane went to check on Rick. The military can be seen in the hospital as I recall.