In "The Sign of the Four" by A. Conan Doyle (1890), Athelney Jones, a police officer, speaks about Sherlock Holmes:
"Your friend Mr. Sherlock Holmes is a wonderful man, sir," said he, in a husky and confidential voice. "He's a man who is not to be beat. I have known that young man go into a good many cases, but I never saw the case yet that he could not throw a light upon. He is irregular in his methods, and a little quick perhaps in jumping at theories, but, on the whole, I think he would have made a most promising officer, and I don't care who knows it."
Could anyone explain the meaning of "...and I don't care who knows it", please?