The sign, in East Road, marks one of the bus stops for Lancaster Royal Grammar School – but has a rather embarrassing spelling error in the word ‘grammar’.
LRGS head Dr Chris Pyle posted the photo on his personal Twitter account with the caption “Umm...”
Many people have responded by jokingly pointing out the irony in such a spelling mistake outside the grammar school.
A spokesman for Lancashire County Council said: "The irony of this unfortunate spelling error is not lost on the county council.”
"Thank you to Lancaster Royal Grammar School head Dr Chris Pyle for bringing this to our attention.
"This schoolboy error does certainly not meet Lancaster Grammar's exceptionally high standards.
"Rest assured, we will correct this mistake and replace the bus stop plates over the coming days.
LRGS head Dr Chris Pyle posted this photo on his Twitter.
"We're glad people have been able to see the funny side and would like to reassure everyone that we will try harder in the future."