Engineering is a combination of technology and art. Therefore, it is impossible to have a simple process for interviewing engineers that magically works. Otherwise, such posts would not have been brought up so many times in HN.
Also, some people are good at people evaluation, some are not. An excellent engineer could be a lousy interviewer. On the other hand, a mediocre engineer is lack of the ability to evaluate a top engineer within an hour. Therefore, the employer must first know who are his/her best interviewers. If s/he can't identify her/his own people, I highly doubt s/he is able to identify good candidates.
The hiring signals I pay attention to are one's curiosity and one's depth in understanding in at least one programming language or one computer science topic, no matter if that topic or programming language has any relevance to the position to be filled. Here is the rationale. To be a very good engineer, one needs both internal motivation and intelligence. Both of the two signals speak for internal motivation. A deep understanding on any topic shows the candidate is sufficiently intelligent. Such a candidate, even if s/he knows little about the languages and/or the frameworks the position requires, s/he would learn it very fast and would be very good at it. To be realistic, it is really not hard to learn a programming language and a framework.