When someone tucks their hair behind both of their ears. It is a sure fire sign that they are attracted to the person they are talking to.
From: Brooklyn Nine Nine, Amy Santiago double tucks whenever she is speaking to a man she likes.
"Aw man, she just did the double tuck, she must really like him."
-"I think she really likes him"
--"But did she do the double tuck?"
-"yup"
--"You're screwed, the double tuck is never wrong"