The sticker on the rear window of Liz Hatfield's Vauxhall Corsa reads: 'Go on small d**k. Pass me.'
But the cheeky message, which has been causing amusement and red faces on social media, isn't meant to be rude.
The sticker has been raising the eyebrows of motorists - particularly male drivers - on the M62
Liz, 47, says the sticker was meant to be an in-joke between her and her partner Richard Buckley, known as 'Dick' from when he worked down the mine.
The sticker was produced to give him a chuckle if he was driving behind Liz, of Fitzwilliam, near Wakefield.
But Liz, a full-time carer, says she understands it could be seen as a challenge - or a threat - to impatient male drivers.
She said: "It was a private joke in case my partner was driving behind me.
"People have taken it as something else and I've left them to it."
And it hasn't just been the public who've taken notice of the unique message.
Liz said: "I've had police threaten to do me for a public order offence but then they went on Facebook and could see my partner was called Dick."
The wording on the sticker, made at a sign printing shop for £20, may have been taken the wrong way but it's had unintended benefits.
Liz said: "I've had it for 13 or 14 months and on local streets I've only been overtaken a handful of times."
She added: "It's definitely slowed a few male drivers down. Women go past though."
While she realises the message could be taken the wrong way by macho men in their machines, Liz has no intention of taking it down.
Liz, who has been on the brink of death twice, said: "I've suffered a lot of ill health so I live every day like it counts; I've got to do."
And the feisty mum-of-two, who dyes her hair different colours each week, has another car with another unconventional message.
A sticker on the rear window of her Volkswagen Jetta reads: 'Faster than a smackhead's giro.'
Liz said: "I just get young people asking me what a giro is."
It's an old word for a benefits cheque, youngsters.