Violet is right. You should say something more than Hi.
I get a lot of Hi's.
I don't understand a hi from someone I don't know.
..I mean, I get it. I do. I would rather, if someone wanted to start a conversation, that they say something more than Hi.
Comment on something I've written. Tell me something about them, and I do not mean their name, age, rank, height, shoe size, or eye color.
Be conversational ~ be silly. tell them something about your day. Ask them questions about what they think about _____. See if they have time for a conversation about whatever that is.