Most people may not get entire sentences, but most people choose phrases that make sense or individual words that are placed so as not to create meaningless phrases.
Dear Bob, the first character is cheng, honesty. The secong is xin, means faith. They're chinese characters, and they don't have to mean something together, people don't get entire gramatically correct sentences tattooed on them. They mean something apart.
This doesn't mean "faith n honesty." The two characters are "sincerity" and "faith," but in Japanese this combination is only used for names: Tomonobu or Seishin. In Chinese it means nothing. The characters aren't too bad, but they're not great either.