Klein said he had been at work for a half-hour when emergency vehicles began pulling into the lot next door.
"We heard the sirens and thought it was a wreck," Klein said.
Firefighters received the call that the store was on fire at 7:32 a.m., and when they arrived, the roof appeared to be ablaze, Hagerstown battalion chief Kyd Dietrich said.
They quickly realized the fire was contained to the sign, but might have cause some roof damage because of the high flammability of the wood, tar paper and other roofing materials, Dietrich said.
By 7:55 a.m., firefighters had put out the flames but smoke still billowed from the roof.
Debra Wible, a manager at Jo-Ann, said several employees were in the back room of the store when they heard the sirens and realized the building was being evacuated.
"They smelled the smoke and left the building," Wible said.
Branden Ingram, 14, had just stopped for a hot chocolate and was walking to school when he saw the firetrucks heading for the shopping center.
Since his mother works at Save-A-Lot in the same shopping center as Jo-Ann, he headed over to make sure she was all right, Ingram said.
Bob Herndon, a manager at Save-A-Lot, said police told him to get everyone out of the grocery store, which was getting ready to open, but they didn't realize there was a fire until they were outside.
"We just heard all the sirens," said Charity Kelley, an employee at Save-A-Lot.
Dietrich said the interior of the store suffered some water damage, and there might be some additional damage from the smoke.
The cause of the fire was determined to be electrical and was related to the sign's wiring, Dietrich said.
Wible said one of her employees reported seeing the store's sign flickering slightly when she arrived to begin work Wednesday.
Employees were allowed back in the store at about 9 a.m., Wible said.
The extent of the damage was being assessed and the store remained closed all day Wednesday, she said.
Jo-Ann likely will be open today, store employee Sal Dambra said. If so, the store will offer the 15 percent discount for seniors that was supposed to be offered Wednesday, she said.