For System z Mainframes, there hasn’t been any formal certifications for some time. Most people would just state their work experience, and possibly any Mainframe courses that they had attended.
IBM has (relatively) recently changed this, with two ‘streams’
<li><a href=”http://www-03.ibm.com/certify/mastery_tests/bd_index.shtml”>Mastery Tests</a> – evidence of mastery of knowledge from a course of learning materials (like the z/OS Basics redbook).</li><li><a href=”http://www-03.ibm.com/certify/”>Professional Certification</a> – formal certification. IBM requires this for some of its partner programs.</li>
However at this stage, these certifications aren’t widely used outside of IBM, and most employers still look at work experience.