"I hope to receive letters from those who are not judgmental and who are sincere," reads the ad, accompanied by a photo of a smiling Smith, 31, wearing sweat pants marked "SC Department of Corrections."
Smith, who is serving a life sentence, gained notoriety in 1994 for going on national television to tearfully plead for the return of her missing sons. She later admitted strapping 3-year-old Michael and 14-month-old Alex into their car seats and rolling the sleeping boys into a lake.
In the $40 advertisement, posted last month on Edgewater, Fla.-based writeaprisoner.com, Smith says, "I will always hurt for the pain I've caused so many, especially my children."
The ad has resulted in thousands of hits and more than 500 e-mails that have been forwarded to Smith, said spokesman Jason Roberts. "Susan is by far our biggest celebrity inmate," he said.
"I love rainbows, Mickey Mouse, the beach, mountains and waterfalls," Smith's ad reads. "I consider myself to be sensitive, caring and kind-hearted. I'm currently serving a life sentence on the charge of murder."
Smith's mother, Linda Russell, said the ad may be a hoax.
But Corrections Director Jon Ozmint confirmed Friday that Smith paid for the ad with a check from her South Carolina Department of Corrections account. Prisoners often have accounts for the small amount of money they earn doing jobs behind bars.
Smith's personal life has made headlines before. Two prison guards were disciplined for having sex with Smith three years ago. One was sentenced to 90 days in jail, the other was put on probation.