I don't know that it's healthy for anyone to walk around thinking there are no good people and looking for signs of Christianity to know whether it's safe to deal with them. Even if it was true and people weren't good at their core, like I believe they are, how does it help to look at them with those eyes?
Isn't all the creation by the hand of one that is good? How can then his creation not be good?
If truth matters (and it does), it "helps" to look at everything as it truly is, and as per a consistently Christian worldview, that includes the total depravity of man--a reality rooted in the Fall of humanity as recorded in Genesis 3. The "total" in total depravity means that all aspects of man have been affected by sin (e.g., the mind, will, etc.) and not that man is as bad as he could potentially be. The gracious, restraining hand of God prevents the latter, and hence, you're not inclined to murder all of those around you right now; you might even wish to do them well.