A MYSTERIOUS art work has popped up on the Bridge St railway line underpass.

An eye-catching teal green and silver stencil work has replaced the graffiti tags.

About a dozen large stencils with the words "relax mort estate" feature along the concreting.

A Toowoomba Regional Council spokeswoman said the council was not responsible for the artwork.

Geoff Holmes from the Safer Toowoomba Partnership co-ordinates the city's graffiti removal.

But even he has been left scratching his head at the mysterious tagging.

Street artist Ian McCallum assumed the stencilling was the work of an organised clean-up crew.

"I have always been interested to put up some legal, proper art in that space," he said.

"It always gets trashed under there."

Mr McCallum said the artwork could possibly be attributed to an out-of-towner.

"It's weird," he said.

"I can't think of anyone, off the top of my head, who would have done it."

Bellevue Hotel Isabella's restaurant worker Cara Rigney said she noticed the painting last week.

"I drove home one night at about 9.30 and there it was the next morning," she said.

 Who is responsible for the artwork? Email anthea.gleeson@thechronicle.com.au