Here's an interesting quote from the YB:
*** yb87 p. 20 1987 Yearbook of Jehovah’s Witnesses ***In India,
a test of integrity came in November 1985 when Witness children in a school in the state of Kerala became a center of controversy because of refusing to sing the national anthem, though they were willing to stand respectfully
*** sj pp. 15-16 Flag Salute, Anthems and Voting ***When national anthems are played, usually all that a person has to do to show that he shares the sentiments of the song is to stand up. In such cases, Witness youths remain seated. However, if our youths are already standing when the national anthem is played, they would not have to take the special action of sitting down; it is not as though they had specifically stood up for the anthem. On the other hand, if a group are expected to stand and sing, then our young people may rise and stand out of respect. But they would show that they do not share the sentiments of the song by refraining from singing.
*** sj pp. 15-16 Flag Salute, Anthems and Voting ***When national anthems are played, usually all that a person has to do to show that he shares the sentiments of the song is to stand up. In such cases, Witness youths remain seated. However, if our youths are already standing when the national anthem is played, they would not have to take the special action of sitting down; it is not as though they had specifically stood up for the anthem. On the other hand, if a group are expected to stand and sing, then our young people may rise and stand out of respect. But they would show that they do not share the sentiments of the song by refraining from singing.