There are indeed two phrases that could come up, "NOW known as" and "NEVER known as". I have occasionally seen "NOW known as" abbreviated to NKA. I've never seen "never known as" abbreviated.
"Never known as", in my experience, is something the singer would write on a signature/name affidavit if one of the names was totally wrong, and not merely an old or misspelled name from a credit report. In that case, after consulting title, the signer writes "never known as" and does NOT sign that incorrect name.