Showing disinterest only works with super hot girls who expect every guy to be falling all over her. Also, it only works if said girl finds you interesting in the first place (ie you're the center of attention, there's other attractive women hanging around you, you're the life of the party, etc).
Showing interest is fine as long as you don't come off as desperate. This works well for all girls, even the hot ones, and you don't need social proof to do it. Just be DIRECT. Talk to women like you talk to your friends. Skip formalities and introductions and all that. If after talking to her for a minute you still think she's interesting, do not ask for her phone number. Ask for a date.
"hey I gotta run, but would you like to go out sometime?"
If she says sure, THEN get her number.
"Ok cool. Let me get your phone number."
You'll rarely get rejected, because you can usually tell just from talking to her if she's interested or not (are you doing all the talking?). And if she says "no/i have a boyfriend/etc" no biggie, just say, "ok, have a good night then."