Mark my words

[Monty]

Phrase said before or after a prediction or declaration to mean: You should write down what I say (mentally or literally), because it will come true or be something [unforgetable].

Usually said in warning or in a betting situation, so that you can win a wager or say [I told you so] later.

Intended to convey great conviction, as though your statement could be [doubted] or denied by others.