sbool signWithComputerIDAndDate_verbose;
sbool signWithComputerIDAndDate_verify;

// appends a new line with computer id and signature
static S signWithComputerIDAndDate(S s, O... _) {
  bool verbose = optPar verbose(_, signWithComputerIDAndDate_verbose);
  S computerID = getComputerID();
  s = rtrim(s) + "\n\n" + "-" + computerID() + ", " + localDateWithMilliseconds() + " (" + localTimeZone().getDisplayName(false, TimeZone.SHORT) + ")";
  s = fromLines(toLines(s));
  if (verbose)
    print("Signing text: " + shorten(quote(s)));
  S signed = s + "sig: " + getMySignatureForText(s);
  signed = fromLines(toLines(signed));
  if (optPar verify(_, signWithComputerIDAndDate_verify))
    assertEqualsOptionalVerbose(verbose, "My own signature", computerID(), getAuthorOfSignedText(signed));
  ret signed;
}