CHICAGO (AP) — Twitter has long been a way for people to keep track of tornado watches, train delays, news alerts or the latest crime warnings from their local police department.

But when the Elon Musk-owned platform started stripping blue verification check marks this week from accounts that don’t pay a monthly fee, it left public agencies and other organisations around the world scrambling to figure out a way to show they’re trustworthy and avoid impersonators.

High-profile users who lost their blue checks Thursday included Beyoncé, Pope Francis, Oprah Winfrey and former President Donald Trump. But checks were also removed from accounts for major transit systems from San Francisco to Paris, national parks like Yosemite, official weather trackers and some elected officials.

Twitter had roughly 400,000 verified users under the original blue-check system. In the past, the checks meant that Twitter had verified that users were who they said they were.

While Twitter is now offering gold checks for “verified organisations” and gray checks for government organisations and their affiliates, it was not always clear why some accounts had them Friday and others did not.

Fake accounts claiming to represent Chicago Mayor Lori Lightfoot, the city’s Department of Transportation and the Illinois Department of Transportation all began sharing messages early Friday falsely claiming that Chicago’s Lake Shore Drive — a major thoroughfare — would close to private traffic starting next month.

A critical eye could spot obvious hints of the fraud. The account handles are slightly different from the authentic ones representing Lightfoot and the transportation agencies. The fakes also had far fewer followers.

But the fakes used the same photos, biographical text and home page links as the real ones.

The genuine accounts for Lightfoot and the transportation agencies did not have a blue or gray check mark as of Friday. Lightfoot’s office said the city is aware of the fake accounts and “working with Twitter to resolve this matter.” At least one was suspended Friday.

A number of agencies said they were awaiting more clarity from Twitter, which has sharply curtailed its staff since Musk bought the San Francisco company for $44 billion last year. The confusion has raised concerns that Twitter could lose its status as a platform for getting accurate, up-to-date information from authentic sources, including in emergencies.

As a tornado was about to strike central New Jersey earlier this month, a go-to account for information was run by the National Weather Service branch in Mount Holly, New Jersey. It had a blue check at the time. It no longer has any check, though the main NWS account and some other regional branches now sport a gray check marking them as official accounts.

Susan Buchanan, director of public affairs for the weather service, said the agency is in the process of applying to get the gray check mark for government agencies. She declined to answer why some regional NWS branches lost their marks and others have them.

The costs of keeping the marks range from $8 a month for individual web users to a starting price of $1,000 monthly to verify an organisation, plus $50 monthly for each affiliate or employee account. But the meaning of the blue check has changed to symbolise that the user bought a premium account that can help their tweets be seen by more people. It also includes other features such as the ability to edit tweets.

Celebrity users, from basketball star LeBron James to author Stephen King and Star Trek’s William Shatner, have balked at joining — although all three still had blue checks on Friday after Musk said he paid for them himself.

For users who still had a blue check, a popup message indicated that the account “is verified because they are subscribed to Twitter Blue and verified their phone number.”