“Safe” meaning safe to the car’s paint. Well?
I suppose the answer depends on how long it’s been applied, and whether it’s sitting on top of actual paint, or the clear coat finish layer, and how oxidized the paint/clear coat layer is.
Just so I’m clear on this, this “bumper sticker” is not on the vinyl bumper or a rear window, but is actually affixed directly to the cars paint?
I’v had good luck with citrus based “Goo Gone” as product that will dissolve glues but not plastics. WD40 will kind of sort of act the same way as a glue dissolver that will not hurt most plastics, but it’s got a few of solvents so there might be a plastic out there it will damage.
If it’s actually directly on the paint you might be out of luck, but you can try sloowwwllyy peeling off a corner of the sticker, and using Goo Gone applied with a Q tip to the glue-paint junction, and see if it will slowly make the glue release as you gently pull on the sticker. Test GG (or any solvent) on an unobstrusive part of the paint before using to see if it damages the paint.
I’ve heard that warming the sticker gently with a hair dryer can help to make it easier to remove.
Another vote for a hairdryer. Then, get someone else to help you, and while one person gently peels away one corner, the other can use a length of dental floss to “saw” underneath and gradually remove the sticker.
Helpful hint–
Before applying a bumber sticker, go down to one of those shops that make magnetic signs that attach to car doors.
Ask for a piece of magnetic material the same size as the bumper sticker, & apply the sticker to that.
I’ve never heard of anybody stealing one of those signs, & it’s cheap & easy to do.
Not a bad idea. However, it does have some limitations. A lot of modern cars have plastic bumpers (I have no idea why, to me a bumper should be able to bump things at low speed without taking damage) and thus the magnet won’t work.
What, that “Bush/Cheney” sticker not seem like such a hot idea now? 
Who cares if you fuck up the paint? “Shit Happens.”
I don’t have bumper stickers, but for the stickers that we’re required to stick on the windshield, Johnson’s Baby Oil works very well.
I used WD-40 to do it a few days ago. Worked very well.
Try one of those orange-citrus based solvents. They work very well on glues and usually don’t harm surfaces.
If all else fails, you can drive the car into something and let the insurance company put a new bumper on. :rolleyes:
WD-40 does a nice job of removing vinyl sticker residue from car paint. Apply some to a soft cotton cloth (something textured like an old t-shirt, to cut down on the lint) and buff at the residue. You shouldn’t have to scrub very hard. Once you’ve gotten all the visible residue, wash the area with with the car wash product of your choice.
If the sticker was applied directly to the paint, there could be some problems with fading–you might see a vague outline of the sticker. A car with a clear coat finish shouldn’t have this problem.
Peanut butter. Spread the PB over the sticker and let it sit over night. The oils in the PB will soften the glue and it will wipe off.
…or a racoon will lick it off, and come around tomorrow night for more.
I vote for the hair dryer trick. I bet it will work. I use that technique when trying to remove unwanted surgeon general stickers off cigar boxes. It works great and doesn’t take the paint with it. Heat the area well and slowly peel from one corner to another. Hope it works for you.
Bumpers are made of soft flexible plastic (or, equivalently, stiff rubber) precisely so they can bump into things without sustaining permanent damage.
In the old days before the Feds madated so-called “10mph bumpers” (later “deregulated” down to 5mph), every time a car struck anything you’d end up with a dent in the shiny chrome bumper. And often the chrome plating then flakes off and rust begins. SO you had to get it repaired promptly.
The plastic ones were a direct effort at consumer protection by providing a bumper that actually achieved its goal of taking a minor impact without requiring expensive repairs afterwards.
I’ve had my Bush/Cheney bumper stickers since last year… they are on the back glass. 