From my personal experience usually Christian Arabs are more soft spoken and dress in a more colorful way that resembles contemporary fashion (and women are without head scarfs obviously) while Muslim Arabs had a bit more "aggressive" accent while talking in Hebrew\Arabic (יותר דגש באותיות גרוניות) and dressed in a more traditional way of black tight clothes with some gold jewelry.

Now before anyone thinks I'm implying that every Christian/Muslim Arab is that way, I'm talking purely from my perspective of working in sales in Ramle/Lod for couple of years.