Behavioral signs that a person is interested in someone romantically include asking questions, finding commonalities, leaning in, and adjusting the body to face the other person. Another counter-intuitive sign is completely ignoring the other person. Social media plays an important role in modern dating, as other signs of interest include adding someone as a Facebook friend or following the person on Instagram.
When a person is eager to keep the conversation going, he is apt to ask a lot of questions to maintain contact. While some questions are for mere politeness, extending those questions beyond casual chitchat may be a sign that someone is interested. When he asks questions without a reason, such as for work or school, it adds to the likelihood that he is interested.
People often seek common interests with someone they are attracted to, therefore punctuating conversation with statements such as "Me, too" and affirmations of agreement. Doing so is an attempt to figure out if the couple is a solid fit.
To avoid rejection and increase the chances that a person takes notice of the person not paying attention, a counter-intuitive sign of interest is ignoring the other person. Someone who opts to ignore another usually is nervous about approaching. After all, if there is no interest, there is no reason to not make small talk.