1. Any company that makes you wait for more than 15 minutes (after you report on time for an interview) is first sign that you are not a priority for them.
2. Whilst waiting look at the energy level, vibe and most importantly faces of the people working there as that will tell you a lot about the actual environment that exists in there.
3. Look at the dates on the magazines lying on the table in the waiting area. Anything that is over a month old and is still there says a lot.
4. If the first point of interviewing contact is a person with considerably less experience than you and he/she takes longer than half an hour with you, this is an indication and a classic case of a company and its HR not having spent enough time going through your profile and knowing the level of experience you have.
5. Most Important, always believe in your first instinct. What you felt about the company in first five minute at the reception area is exactly what is true.