Not a milestone per se. Not to anyone but us, your family, because a) we're over that little expected behavioral "hump" (heading speedily toward the terrible two's) and because you have finally (finally!) gotten your eye teeth--those terrible pointy teeth with literally longer roots than wisdoms.
One little vignette provides a decent overview of month nineteen.
A few nights ago you were having a hard time falling asleep. I'd put you in the crib and walk away, fingers crossed, and you'd howl. We're quite empathetic with this behavior since it usually signals a problem on your side of the equation. In this case, as we expected, it was your impending teeth.
The third time I went in, I picked you up out of your crib and held you, humming a little comfort song, hoping you'd relax a bit.
You hooked your left arm around my neck and held tight.
As the song neared its end, you leaned back and emphatically and repetitively made the ASL sign for "more!"