The phrase "a petition was signed" is correct and usable in written English.
It can be used when referring to the act of formally endorsing a request or appeal, typically in a legal or civic context.
Example: "After gathering enough support, a petition was signed to request changes to the local zoning laws."
Alternatives: "a petition was endorsed" or "a petition was executed."
A petition was signed by several senior staff members, demanding full transparency and media freedom.
A petition was signed asking the council to reconsider its policy.
She had always wanted the British government to apologise, and in 2005 a petition was signed by more than 10,000 people.
Wicked Campers did issue an apology after a petition was signed by over 100,000 people in 2014, and publicly agreed to remove the offensive slogans.
They were pardoned two years later after their cause became a national campaign, and a petition was signed by 800,000 people.
There was a subsequent campus protest at Harvard, a petition was signed (I can't remember if I signed it), and soon afterward the Harvard Athletic Association announced that Harvard would never again withdraw a player for reasons of race.
From time to time, a statement or a petition is signed by a group of people, though they usually take pains to present themselves as an assortment of individuals, rather than as an organization.
It's likely that you were already aware on some level that the war on marijuana is a racist disaster ending the war on drugs has become such a mainstream cause in the past few years that a recent petition was signed by a host of A-list celebrities.
The conservative member for Epping, who has previously dubbed the program a "Trojan horse", said the petition was signed by people from across Sydney, not just in his electorate.
Another, more temperately worded petition was signed by a list of French celebrities, including actress Catherine Deneuve, who played a prostitute in the 1967 Luis Buñuel film Belle de Jour.
The petition was signed by over 220,000 people.
