The message was found Friday at the makeshift memorial outside the 84-year-old's Catalina Foothills home, more than three months after she disappeared from Tucson.
It tells the abductor that their mother would be ashamed and urges them to take Nancy home or tell her family where she is before Mother's Day on Sunday.
It is unclear who left the unsigned note, which adds a new public appeal in the still-unresolved case of Savannah Guthrie's missing mother.
Why has a $1.2M reward failed to break the silence in Nancy Guthrie's kidnapping?
With DNA and video evidence, why do investigators remain stumped months after the abduction?
Could the abductor's 'mistakes' be a deliberate misdirection by a sophisticated criminal?