You normally don't see it. It used to be a lot more commonplace, but now the services have done away with requiring members to wear their uniforms during travel. I think the Army and Air Force were the last ones to do away with it unless it is under certain conditions. But he may have been wearing it because he only had a short time to get from the airport to the event he was attending. And I assume he is out of the Marine Corps because his uniform tells me. But upon Honerable Discharge from the Marine Corps you are authorized to wear your uniforms for life.
"What country can preserve its liberties if its rulers are not warned from time to time that their people preserve the spirit of resistance?" -Thomas Jefferson-
"Our rights come from our humanity and may not be legislated away -- not by a vote of Congress, not by the consensus of our neighbors, not even by agreement of all Americans but one." Judge Andrew P. Napolitano