Signs and Indicators a Face to Face Interview Went Well
Firstly, it is important realise there is no 'guaranteed' sign or indicator that tells you that a face to face interview went well -- unless you are practically told you have the job/internship/college position, right there and then in the interview. But, there are both positive and negative signs in an interview that you can judge to potentially roughly estimate how well/bad the interview went. Most of the positive and negative indicators you can look out for in an interview are listed below -- but one last point worth recognising is that like all interviews -- you are likely to come across better/worse in particular interviews to different interviewers, given all else equal i.e even if you had performed the exact interview -- one interviewer might have thought the interview went well for you whereas the other interviewer many have thought the face to face interview went poorly for you (hence a rather subjective process - it is not absolute)... Just because you feel that some of the points below came off -- does not mean that your interview went well in the interviewer's eyes (that is not to say the interview went poorly either).
Furthermore, ultimately you don't really know where you interview performance stands against other applicants -- you may have had an interview that went good with positive signs, however your competition might have done just that bit better. (There is a skill in face to face interviewing -- reading and studying books on improving your interviews is likely to enhance that skill. Great books on interviewing I personally like are the 101 Great Answers to the Toughest Interview Questions by Ron Fry and also the 'Headhunter' Hiring Secrets: The Rules of the Hiring Game Have Changed . . . Forever! by Skip Freeman.)
So how to know if your face to face interview went good? - The Signs and Indicators
The Body Language of the Face to Face Interviewer - obviously unlike trying to tell if a phone interview went well -- you are able to analyse and see the signs of the interviewer's (often subconscious) body language. Positive indicators to look out for would in general be displays of interest or IOI (indicators of interest) -- they give you regular eye contact, sit up straight, often nodding their head and smiling with agreement to the answer you have provided (often accompanied with a scribbling down of notes -- usually if they are taking down notes this a good sign, otherwise if they close the book it shows they are either not really listening or they aren't interested in you) -- in no particular order. There are a few negative body language indicators to also check for which may have indicated that the face to face interview went bad (1st .many of the opposites of the above e.g. closing their notebook) -- such as the regular checking of time, the more the interviewer is looking up at the clock or at his/her watch, the more they are interested in keeping to the interview time constraint rather than on the actual interview and you. You need to keep their attention on you, also if they are doing anything but talking to you and interviewing you (whether that be checking, emails, answering phone calls -- the less likely they are to be interested) then that can be taken as an IOD (indicator of disinterest) and reflects negatively on your interview performance. Edit: yawning and poor posture.
The Questions Asked - you can determine a fair bit of how the well the face to face interview went, by the actual questions being asked. You can determine whether they are listening attentively as to whether the actual questions asked are specific (and not generic) to the answer you have given -- obviously if you have been asked these type and style of questions, these are positive signs that the interview is going well. Furthermore, a real positive indicator to take away from a successful face to face interview would be any 'job related' questions -- where questions were being asked about the responsibilities you would undertake, or whether they are asking for references, anything that involves 'further engagement' almost like questions that are passed the interview stage -- they ask about salary expectations etc. If they refrained from 'job specific' questions, or did not ask you to take an extra step in the procedure and asked rather generic questions then this could mean you perhaps did not perform well in the interview or were simply not the right candidate for the role.
Demonstrated You Were an Exceptional Candidate - from books such as the above, and interview educational videos such as in Ramit Sethi's I Will Teach You To Be Rich blog (e.g. the brief case technique video) -- you will learn how to present yourself (and actually be) as an exceptional candidate for the job on offer. Where you can demonstrate that you fill all the minimum requirements of the job role, but also 'then some'. E.g. from company research that you have conducted -- you have identified the company's website weaknesses (e.g. SEO, poor navigation) and presented how you could fix them, and what this could mean once they are fixed. Already demonstrating that you have the potential to be an integral part of the company. If you have presented yourself in a similar manner/style and the interviewers appeared to be engaged with what you had to say -- this obviously is a strong indicator that your interview went well.
The Longer... the better - In relation back to an earlier point made about checking for the time, the fact that the interview went longer then it should have done is a also positive indicator of interest in you as a future potential employee. It makes practical corporate sense -- an interviewer is going to spend more time with a candidate that they think are just right for the role, clarifying any minor issues etc. than that of a potential candidate who they don't feel to be right for the company or role, as it would be a waste of resources.
Summary of How to Know if a Face to Face Interview Went Well
The signs above of whether the face to face interview went well or if the face to face interview went bad -- are exactly that 'signs' -- if you feel you had more negative signs and indicators that doesn't necessarily mean your interview went bad (and vice versa). Again, the only real way you know your personal interview went good is if you eventually get the job. If you don't get the job -- I would encourage you (I know it can be difficult) to get back in touch with them and ask for some constructive feedback on your interview performance and take in the advice and practice on your interview technique (if wasn't a technicality/experience issue).
It is important not to dwell (which I have been guilty of many times) on a bad interview performance as you can only do better the next time, pick your head up and practice. Hopefully, this article has been useful to you in trying to determining how to know if your face to face interview went well, if you know of any additional signs or indicators, or experience of face to face interviews then I encourage you to please leave a comment below.