WASHINGTON (Reuters) - President Barack Obama volunteered at a local school on Monday to mark the Martin Luther King Day holiday, testing his talents as a painter while emphasizing the importance of community service in America.

Obama, who was joined by his wife, Michelle, and their two daughters, helped out at a middle school, where volunteers were painting "dancing fruit" on the cafeteria walls to encourage healthy eating habits.

Obama painted an apple that looked like a cartoon character flexing its muscles.

He said the event helped remind people about true U.S. values after the recent shooting in Arizona that killed six people and wounded 13, including a U.S. congresswoman.

"After a painful week where so many of us were focused on tragedy, it's good for us to remind ourselves what this country is all about," Obama told reporters in brief remarks at the school.

"This kind of service project is what's best in us and we're thrilled with everybody who is participating."

Volunteers serenaded the first lady with a version of "Happy Birthday" after she entered the cafeteria. Mrs. Obama, who turned 47 on Monday, seemed touched but embarrassed by the song.

"All right let's get to work. This is embarrassing," she said. The first lady has made fighting childhood obesity one of her signature issues since coming to the White House.

(Reporting by Jeff Mason)