From me James.
Please remember people that one of the "lead principles" in camouflage is to break up the regular shape of an equipment item, (in this case, the helmet), as well as reducing "shine" and "silhouette"
I would also agree that the "Int sect" refers to Intelligence, and "D-coy" obviously refers to D Company of whatever battalion the previous owner was a member of. I cant give you any clues as to when the service number was issued, other than to say my first four are 2461 and I was given that number in 1981!!