People will say thank you cards are unnecessary after an interview and some recruiters even say that thank you cards sway them one way or the other. But I would argue that even if you don’t get the job HR people will always remember those who send them a thank you card and maintain contact with them. Thank them for their time, remind them about something you chatted about, and show that you appreciate their consideration. Write it immediately after the interview and either drop in a mailbox or give to the receptionist to hand in for you. Nothing too flowery or long, and make sure you sign your last name as well.