HAHAHAHA do not wear a pocket square. its an interview not a fashion show.
EDIT: I apologize, that came off mean. IMO, pocket squares are an accessory that takes a lot to pull off. Therefore, it is safer and more conservative to just skip the square. If you look like Brad Pitt and have the confidence to back it up, wear a pocket square because you can pull it off. But if you have to come to a forum for an opinion, I feel like you will be worried about it during the interview, (if they are looking at it, if they disapprove), which will show on your face and thus affect your interview demeanor.