How to tell if the other person is serious in the relationship

They will invest themselves in the relationship; give their time, energy and emotion to it.

They will talk about future plans

Their parents and close friends know about you

They stay in touch, and do not dissapear for days without notice or communication

They take an interest in what you like/dislike/have to say. The conversations do not only revolve around them

You dont have other people telling you that 'he/she is bad news. Stay away' Like they say,where there is smoke, there is fire.

Your gut feeling, trust it. When the other person is not sincere, it shows; through eyes, thoughts and words, but sometimes we are too hazed by love to see or feel it.