It is illegal to take a car's hood ornament if it is not your car. This is considered theft, as you are taking someone else's property without their permission. It is also a form of vandalism, as you are damaging someone else's vehicle. The penalties for theft and vandalism vary depending on the jurisdiction, but you could face fines, jail time, or both.
In addition to the legal consequences, there are also social consequences to consider. If you are caught stealing a car's hood ornament, you may be publicly shamed or even fired from your job. It is not worth the risk to take someone else's property. If you want a hood ornament, you should purchase one from a reputable dealer.