Steve - you've got me there - that one has gone straight over my head. Please elucidate?
AD28 - or Alfa Delta 2 8
Its the NATO signal code for 'Splice the Mainbrace'. (and its actually in NATO tactical publications). Its the signal used nowadays when ordering ships to issue a tot of rum to each crew member.
The name splice the mainbrace comes from sailing times. The line to trim the sails was called a brace. The brace would run from one end of the yardarm to the other, and then straight down. It was easily one of the hardest jobs if you had to go up the mast and splice the main(sail)brace(especially in battle). If you did it, you were given a double issue of rum.
Nowadays, the official signal AD28, is used sparingly, but when it is used, the flag signal AD28 (seen here) will be hoisted, and all ships crews will line up waiting for their tot. (tot being 2 and a half ounces of overproof dark rum) You can drink your tot neat(straight) or you could have it as grog (watered down, perhaps with a little lime juice and sugar).
I am hoping that my old Canadian Naval Reserve unit, HMCS HUNTER, might be celebrating the battle, because she holds HMS HUNTER's battle honours, and I believe the namesake ship was at Trafalgar.