What Is The Meaning Of The Small Cross Tattoos?

Two of my parents friends, both guys, about 45 years old have the same small - i'm talking 1 inch - cross tattoo.. It's as simple a design as you can get, two intersecting lines.. I'm not even sure if they're ''real'' tattoos, they look like they were done with a more traditional - sort of tribal - type method. One of them has it on his forearm, the other his middle finger.
So what does it mean? I've heard some things like gang or drug affiliations, which is a possibility..but it's definitely not the whole 'they killed someone' thing. Does anyone know what I'm talking about?

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