For me, the tell-tale sign is a demonstrated lack of understanding of type theory. Like calling toString on string objects. Or even worse, calling parseInt on a string that was created by calling toString on an integer!
Also, comments-used-as-source-control. If I see one more gigantic block of code commented out with a set of initials and a date "this was removed by/on". Use the source control to do that, dammit.
Also, comments-used-as-source-control. If I see one more gigantic block of code commented out with a set of initials and a date "this was removed by/on". Use the source control to do that, dammit.