Hoards of trick-or-treaters will roam the streets tonight demanding candy from any who come in their path. But centuries ago, God-fearing Britons believed that actual witches and spirits wandered the streets, leaving death and misfortune in their wake.

The fearing citizens carved symbols known as “witches’ marks” on their doorways and window frames to ward off the malicious spirits ― and today, a heritage agency wants the public’s help to record the whereabouts of these magical symbols.

In honor of Halloween, Historic England put out a call on Monday asking residents to send in photos and locations of carvings believed to be “witches’ marks.” A short video, below, posted on the agency’s website explains some of the history behind the marks:

“[Witches’ marks] were such a common part of everyday life that they were unremarkable and because they are easy to overlook, the recorded evidence we hold about where they appear and what form they take is thin,” Duncan Wilson, chief executive of Historic England said in a statement. “We now need the public’s help to create a fuller record of them and better understand them.”

The marks are apotropaic symbols, a form of iconography derived from the Greek word for “averting evil.” They can be found in caves, barns and on houses dating from roughly 1550 to 1750. There’s even a witches’ mark inscribed on the house where Shakespeare was born, the agency said.

The marks commonly take the form of a “daisy wheel,” or hexafoil, which the agency said was used to confuse and entrap evil spirits. Others were carved in the form of letters, like M for Mary and VV, for Virgin of Virgins to call upon the Virgin Mary’s protective power.

Here you are #HistoricEngland. #witchesmark on my #inglenook. Some might say it hasn't done its job A photo posted by Caroline Donald (@pacets) on Oct 31, 2016 at 1:25am PDT

“Witches’ marks are a physical reminder of how our ancestors saw the world,” Wilson said.

The early modern era was marked by superstition and witch hunts across Europe. Under King Henry VIII, the UK Parliament passed the Witchcraft Act in 1542 to make witchcraft punishable by death. It was repealed and reestablished in the years after, and accusations against witches peaked in the late 16th century. The Parliament’s website estimates that some 500 people ― most of them poor, elderly women ― were executed for witchcraft in Britain.

#witchesmark - They'll be out and about tonight! #happyhalloween #apotropaic 🔮🕷👺 A photo posted by Sascha Way (@saschalway) on Oct 31, 2016 at 6:04am PDT

What seems like unfounded hysteria in retrospect may have been an earnest fear of malicious forces for average Britons battling disease, famine and a changing world.

“[Witches’ marks]... can teach us about previously-held beliefs and common rituals,” Wilson said. “Ritual marks were cut, scratched or carved into our ancestors’ homes and churches in the hope of making the world a safer, less hostile place.”