From kill:

If SIGNAL is either the number 0 or the string ZERO (or SIGZERO ), no signal is sent to the process, but kill checks whether it's possible to send a signal to it (that means, to be brief, that the process is owned by the same user, or we are the super-user). This is useful to check that a child process is still alive (even if only as a zombie) and hasn't changed its UID. See perlport for notes on the portability of this construct.

I wonder if that's what you mean by "running status".