I put to blue dots on one side of the ball.

I mark all of my Titleist balls with 1 black dot on each side of the number and on each side of the ball.  I also mark a thin black alignment line on the equator.  I love the way my Pro V1x's perform!

I have a Shamrock Stamp that I put under the # on each side.  

I just started doing this two weeks ago, but I now mark my ball on both sides with a + on the dimple right above the middle of the Titleist logo with a light blue sharpie. Gives me a target, and also reminds me to stay positive with my shot.

Four blue points showing a "C" and a blue alignment line

Just a simple dot next to the Titleist script with a purple sharpie.