The signal book of 1806 has signals for message start (red and white diagonal) and for message finished (blue and yellow diagonal).
Admiral Pophams signal book of 1806.http://www.scribd.com/doc/14245050/Admiral-Pophams-Telegrap-Signal-Book-1806
Signal "16" and "39":
The signals were from the Admiralty Book of 1799.
16. Engage the enemy more closely.
1. yellow over red over yellow.
6. diagonal from lower hoist to upper fly, white over blue.
39. Discontinue the action.
3. blue / white / blue.
9. blue over white over red.