The 18-year-old Disney star - who checked into an undisclosed facility earlier this year for "emotional and physical issues" - says she had the heart inked on her wrist to remind her of those who gave her the strength to remain positive during the dark time.
She said: "The journey that I went through and the support of my fans was so meaningful to me that I wanted to thank my fans in a way that I know can never be forgotten.
"So I went ahead and I got a little heart tattoo on my wrist."
The brunette singer - who recently reunited with her ex-boyfriend Wilmer Valderrama - also revealed that some of her fans have the same tattoo and that she feels connected to them through having the body art done.
She said in a video appearance on website campio.com: "It's something that my fans were actually drawing on their wrists while I was still in treatment. Some people even got tattoos of it, so I wanted to show you guys that I will never forget the support that you guys gave me."
"I will look at it every day and remember you guys and be completely thankful for you."
Demi entered rehab voluntarily at the beginning of November 2010 after an incident in which she allegedly punched backing dancer Alex Welch.
In December she settled her dispute with the dancer by giving her a sum of money in compensation.