Economic historian Dr Helen Paul, of the University of Southampton, found the hand-written message when she was removing the packing stitches from the kilt, which has been passed down her family over decades.
The message reads: "I hope your kilt will fit you well, & in it you will look a swell. If married never mind. If single drop a line. Wish you bags of luck, & a speedy return back to Blighty."
Underneath was the name of Helen Govan, of 49 Ardgowan Street in Glasgow.
The London Scottish Regiment kilt, manufactured by Peter Wilson of Bridge Street in Glasgow, would have been made for use by a soldier sent to fight in the war, but for reasons unknown, it was never unpacked or worn.
Dr Paul is now hoping to find the descendants of the seamstress to uncover the story behind the note.
She said: "This garment has been in our family for a number of decades, and until recently, we were completely unaware there was such an intriguing secret hidden in its folds. It was a real surprise when the note fell out.
"My father tried to trace any relatives of the note's author a few years ago, but his efforts failed and I'm hoping to pick up where he left off.
"There are many unanswered questions. We don't know how many of these poems this lady sent. Was this a one off, or were there many more lost to the battlefield, or even still existing undiscovered? If there were more, did anyone ever answer her message and indeed did she ever meet and marry a soldier returning from the war?
"It would be fantastic to trace who this lady was and learn more about her history, as well as the social history of the women who made and packed the kilts, which ultimately went to clothe the soldiers fighting in the trenches."
Professor Maria Hayward from the University of Southampton, who specialises in the history of clothing, said: "The condition of the kilt is very striking - you do not expect to see a piece that has such clear links to the First World War being in such good condition.
"The construction, which is very simple, in combination with the efficient use of fabric and the way one size could be made to fit most men, made kilts of this type a very versatile piece of military uniform, which also retained its distinctive national identity."