mark my words
(idiomatic) Listen to me; used before or after a statement one wishes to emphasize, especially a prediction.
Women are going to lead the democracy movement, mark my words. George W. Bush
The worst food you'll ever eat will probably be prepared by a 'cook' who calls himself a 'chef.' Mark my words. Alton Brown
My mom's gonna be the biggest star - mark my words right now! Vinny Guadagnino
Ah, this is the constitution, he said. Now, mark my words. So long as we are a young and virtuous people, this instument will bind us together in mutual interests, mutual welfare, and mutual happiness. But when we become old and corrupt, it will bind no longer. Alexander Hamilton