Registration opened Tuesday morning for Scotch Plain and Fanwood's second annual Martin Luther King Jr. Day of Service, sponsored by the Scotch Plains-Fanwood Ministerium. Calling for "a 'day on,' not a day off,' " the Day of Service is a nationwide event that seeks to unite communities through volunteer activities. At Scotch Plains and Fanwood's inaugural Day of Service last year, more than 500 volunteers participated in over 30 community service activities. "There have been few moments in my life as powerful as standing in front of over 500 people who took their time to make a better world…