We need to remember what articles are for. "A" is used to speak about something that exists, and that we are mentioning for the first time and/or it is one of many of such entities. "The" is used to speak of something that exists, and that we have already mentioned previously.
However, if there is no sign of life somewhere, there is not an entity to speak of. So "no" provides some pretty specific information—that something is absent; so it's a determiner of its own.
A similar phrase would be
There is no reason to believe that our information is incorrect.
There is no way to help him.
(If there were one, we'd say, "I know a way to help him"—one of many possible ways.)