It may just mean it's not indexed yet. How long has the site been active? Was it showing results for site:domain.com before? Do you have reason to suspect it might be banned? You are right it is one indication, but not a certain indication.
how old is the site? if you can't really see the site by any means, then it may not yet indexed or it was banned..
site is about a year old;it was index fine and it has page rank and backlinks. but all of sudden it is not in the index nor it is searhable