Elon Musk's X, formerly known as Twitter, is facing a bill from San Francisco authorities after placing an unauthorised flashing X sign on the roof of its headquarters.

The sign was put up on Friday as part of the company's rebrand, but it attracted 24 complaints at the weekend.

It was taken down on Monday and X will be charged the cost of building permits for its installation and removal.

San Francisco authorities said the firm did not have permission for the sign.

In a statement, officials said the company would also have to cover the cost of the Department of Building Inspection and the Planning Department's investigation.

X Corp has been approached for comment.

It is not the first obstacle Mr Musk's company has run into as it changes its downtown headquarters.

An attempt to remove the firm's old name had to be temporarily abandoned, meaning for a brief period only the letters ER remained on the building.

Wider questions have also been asked about the wisdom of abandoning one of the best known names in tech - and killing off the blue bird logo with which it was synonymous.

Mr Musk and the firm's new chief executive Linda Yaccarino want to transform X into a so-called "everything app", where they hope users will want to spend more of their money and online lives.

So far the only changes have been cosmetic - with the X symbol replacing the blue bird on both desktop and mobile versions of the platform.