Decal or no decal, that's like saying, take your rims off so people won't notice your car. That's what insurance is for. Someone steals shit, sure it's a hassle, but it's covered. I wouldn't change my car a bit except for an alarm just b/c some would-be thieves. Chances are, they will get you anyways. My car had no decals when they stole shit from me. It had rims and tail lights, and a cheap intake. They don't look for decals. After all, people do load stock cars down with decals to try and look modded. Thieves don't trust decals anymore really I wouldn't think. It's all in how your car looks, not about decals. If it looks modded, decals or not, they know chances are it has some stuff they can steal.