Step 1. be a victim.
Step 2. be a good witness while you are being a victim. We'll do nothing with this information but take a report.
Step 3. if any violent scumbags are ACTUALLY apprehended as a result, rest assured they will be released within 24 hours.
So, how does complying with an armed assailant, and hoping that they truly only want your property, "prevent" a carjacking?