The revocation of the registration of SIOR stock was not voluntary unless you consider not filing required periodic reports and not responding to an SEC Administrative proceeding to revoke the stock be a "voluntary" revocation. IMO, it is more like voluntary abandonment by the officers and directors.
Links that show SIOR was suspended and then revoked by the SEC (not volunary):
The registration of SIOR stock was suspended and then revoked in the same way that hundreds of other companies with registered stock have been suspended and revoked for failure to file periodic reports with the SEC.