Use a label. If you want it to look more like a comment, you can set the icon to blank.
I don't think there are any settings directly on the step, but you could create a custom "Step List Configuration" that looks for steps of the label step type and changes the color or font setting based on that.
As far as I can tell you can't change it. You can however try to accomplish it by using a custom step type that has a larger font. I hope that this helps.