[EliRivers]

Is there a way to look at girl in a cute pink dress and tell whether she is there to just present a tech topic or she is also open to potential dating?

No.

You're asking too much to be reliable able to look at someone and know if they're open to dating. Given that your target demographic is about 50% of the world's population, the variation is just too large for you to be able to do this. You're going to have to try something else.

Perhaps a polite, friendly conversation and a sustained programme of getting to know them will help you know if they're open to dating.