The locket, which contained a tress of Lizzie Walmsley's hair, also had her name engraved on it. Halliday was carrying it with him when he was killed in action in the last days of the war at age 22, ending their dreams of building a life together.
But that pre-war romantic gesture would prove vital in identifying Halliday's remains, and giving him a burial with military honours nearly 100 years after he was killed in battle.
Halliday is one of eight soldiers whose remains were interred Wednesday in a military funeral, joining several of their fellow members of the 78th battalion, also known as the Winnipeg Grenadiers, resting far from home — and ending a century-long search for families they left behind.
Killed in one era, now honoured in another, the eight soldiers were laid to rest by soldiers generations younger, watched by family members they never met.
But the feeling of loss spans time.
"He always seemed to be a presence," an emotional Jim Halliday, his nephew, told CBC News. "There were pictures of him around and his medals we had. He was just part of the family in a way."
"I'm just so grateful that he and all the rest of his friends there have the place they deserve."
The Hallu 8
It was a quiet ceremony at a tiny British war cemetery in Caix, France. Fellow Manitobans — members of the 2 Princess Patricia's Canadian Light Infantry — carried the caskets on their shoulders in a slow march, before gingerly lowering them into the ground.
"To participate in a soldier's funeral is a tremendous honour … doing it for legends of World War I is quite an honour," said Master Cpl. Mackenzie Murphy.
Also attending the funeral on Wednesday was a young Frenchman by the name of Fabien Demeusere, who found the remains of the Canadian soldiers in 2006 while digging in his backyard in the village of Hallu.
His discovery kicked off an extensive hunt for their identities, using DNA testing and historical research. Five were ultimately identified: Lt. Clifford Neelands; Lance Sgt. Oscar Lindell; and privates William Simms, Lachlan McKinnon and Halliday. Three others remain unknown. They became known as the Hallu Eight.
According to National Defence, it is the largest single find of unknown Canadian soldiers since the start of a casualty identification program in 2006.
The department says the soldiers were killed while trying to hold ground in Hallu on Aug. 11, 1918, during a decisive battle that claimed 100 Winnipeg Grenadiers as dead or missing.
Demeusere was presented with one of the carefully folded flags, normally reserved for family members, which had covered the casket of one of the unknown soldiers.
It has been an emotional journey for Jim Halliday. The trip from his Manitoba farm included a stop in France Lynch, the English village where his uncle was born, and where a pub is still run by his family.
He and his wife Pat met there with British relatives who also provided DNA to help identify the remains.
"We spent a lot of time in the archives … and asking around the family for all sorts of birth certificates, marriage certificates, and so on," said Christine Gibbons, wife of Don Gibbons, who is Sid Halliday's third cousin.
But Veterans Affairs said the genetic testing wasn't conclusive, and seemed a dead end. It was the locket found next to the remains that provided the proof: showing a partial engraving that Jim Halliday recognized as the name of his uncle's sweetheart.
The locket was cleaned up and presented to Halliday on Wednesday — with the lock of hair still intact: a reminder of an uncle he too loved, though he never met.
"I cannot tell you how much it means," said Halliday.
National Defence says there are still 28,000 Canadian soldiers killed at war whose remains still haven't been found.