// appends a new line with computer id and user signature
static S signWithUserID(S s) {
  S computerID = getComputerID();
  s = rtrim(s) + "\n\n" + "-" + computerID() + " [user]";
  s = fromLines(toLines(s));
  S signature = s + "sig: " + getUserSignatureForText(s);
  signature = fromLines(toLines(signature));
  ret signature;
}