WOODLAND HILLS, Calif. — Every day for the last 15 years, Luke Shaft has been going to his neighborhood gym with one goal in mind: transforming himself into the ultimate fighting machine. 

But Shaft is not doing it for vanity or bragging rights. He’s doing it for his grandfather. 

“Hearing the pain that he went through and feeling like he didn’t have an option in the darkest hours made me find a way to give me courage and strength,” Shaft told Spectrum News 1. 

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His grandfather, Louis Berliner, was a Holocaust survivor. After the Nazis murdered his entire family, Berliner was sent to Auschwitz, where incoming prisoners were tattooed with a serial number.

He eventually made it to the U.S., where he went on to have a wonderful life, Shaft said. 

But that tattoo with the numbers 138486 was a permanent reminder of the atrocities he endured during World War II.

When Shaft turned 18, he decided to honor his grandfather by getting that same number tattooed on his own arm.

“Any time I think I feel pain or sadness, or anytime of despair, I just look at that and think, 'I don’t know anything of these feeling,'” he said. 

Shaft is one of a growing number of descendants of Auschwitz survivors who have taken the controversial step of memorializing one of history’s darkest moments on their own body.

The practice, which has been gaining momentum in both Israel and the U.S., has been criticized for re-appropriating a Nazi symbol meant to dehumanize its Jewish victims. 

But Shaft doesn’t see it that way. 

“A lot of survivors and a lot of people are ashamed of speaking of what happened because of the atrocities," he said. “I don’t think it should be kept a secret. I don’t think it should be held back, I think it should be put out into the public. I wear it very proudly.” 

A new survey suggests fewer and fewer Americans know the death toll Jews suffered during the Holocaust.  

The Pew Research Center report, “What Americans Know About the Holocaust,” shows 45 percent of almost 11,000 Americans surveyed didn’t know the Nazis killed 6 million Jews during World War II.

The study comes as the world commemorates Holocaust Remembrance Day, which the year coincides with the 75th anniversary of the liberation of Auschwitz, where more than a million Jews were murdered. 

It’s hard to say how many people have followed in Shaft’s footsteps. 

Cathy Fischer, is Shaft's cousin and a filmmaker. She's been working on a documentary about this phenomenon called, Under Their Skin: Tattoos of Memory and Resilience.

She said that during her research she found at least nine people in her immediate circle — all third-generation survivors —  who have tattooed their relatives’ number on their bodies, including Shaft’s brother, Max. 

“The grandchildren feel like they are transforming the tattoo and showing it as a badge of courage, a symbol of survival, the best revenge," she said. 

Shaft’s grandfather, Louis Berliner, passed in 2009. But not before he and his wife, also a survivor, gave Shaft their blessing.

"They both cried and they touched it as if it were some sort of monument to the Jewish people so it was a very special day,” Shaft said.