I saw a bumper sticker of a giant rat with the word “Baltimore” on it. I know Baltimore is well known for it’s giant rats. It just seems weird to me that people would advertise it.
I saw a funny variation a couple of years ago: " Lord, help me be the person my enemies think I am".
Not a bumper sticker, but an advertising slogan in big letters across the rear and sides of a delivery box truck seen today.
You want some of
what we’re smokin’
They smoke fish as in making salmon into lox.
But - do they make Sable?
So hard to find these days.
I have no idea; What I know is the artwork on the truck included a pic of a vaccum pak of smoked salmon.
ETA:
Upon further review …
Although based in NYC, they have an outlet here in South Florida. Of course they do; half of NYC lives here part time. And the other half lives here full time.
And they do have Sable. And Whitefish. And …
And you can buy a sweatshirt with their slogan on it. 
I have no pictures to back this up, but recently my husband spotted a “murderino” decal on the bumper of the car in front of us- it was the tagline for the true crime podcast My Favorite Murder, aka: SSDGM/ for “Stay Sexy and Don’t Get Murdered “. He didn’t know what the acronym was so he guessed. “Same Shit, Different GrandMa”? Automatic spit take from me! 
My sister used to live in an old row house in the Canton area. She referred to them as city kitties.
The other day, I saw a car with so many of those oval, three-letter stickers, they covered the back and started wrapping around the sides. I’m guessing they’ll never try to sell that car.
When Food Town supermarkets was in the process of changing its name to Food Lion, it issued bumper stickers with Town crossed out, and replaced by Lion. However, the cross out marking and the word Lion was written in yellow ink that faded in sunlight, leaving just the words Food Town, written in unfaded red ink.
I was driving behind a Tesla a few weeks ago with a bumper sticker that read:
“Well…THIS is Awkward”
Beautiful!
Yesterday I saw a parked SUV whose rear surface was just about plastered with separate 1" tall stick-on letters they’d used to make various slogans. Lotta effort, and apparently this person is taking their anti-trump activism seriously. Good for them!
My fave said:
If you put a clown in a palace he doesn’t turn into a king. Instead the palace turns into a circus.
We don’t do bumper stickers over here, but we do write in the dirt on the back doors of panel vans.
“I wish my wife was this dirty” is a perennial favourite.
As I mentioned in the license plate thread, last week I saw “Jesus saves, bro” in the rear window of a 4Runner. Bro? To me that reads like a lame attempt to make Jesus sound hip.
And on the complete opposite end of the spectrum, yesterday I saw “I’m so gay I can’t even park straight”.
I’d buy it.
To pretend you went all those places?? 
Along I’m sure with the old “Wash me”.
To avoid that kind of thing I’m told there’s a bumper sticker with the legend “I don’t wash it because I love my native soil!”
“Jesus saves. Gretzky gets the rebound; he shoots, he scores!”
“Jesus saves, Moses invests”
“Jesus Saves, Buddha and Mohammed take full damage”