Today is Labour Day, also known as International Workers' Day and May Day. It is the day most labour unions celebrate around the world.
To see all the countries celebrating today, see Wikipedia.
Google has a special logo for the day, of a man with his tool box holding up a steel Google sign. How worker like!
The U.S. doesn't celebrate labor day today, although there have been many efforts to change that.
So if you do not see a logo for Labour Day on your Google, it might not be celebrated where you are.
Forum discussion at Google Web Search Help.