Martin Luther King, Jr. is actual birthday is 15th January but in the US it is officially celebrated each year on the 3rd Monday of January. It's a national holiday. So, earlier on Monday the hashtag #MLKDay was trending. I could download around 110K tweets. Not surprisingly, the most common word is MLK. Many positive words show up frequently - happy, goof, celebrate, dream, legacy, equality, honor, love, right, justice, etc. His most commonly cited lines "I have a dream" must have appeared in many tweets, explaining why "dream" shows us so often. There was a hashtag for "ihaveadream", which shows a few times. Overall the sentiment was very positive.