The first markings would probably refer to the parachute used for the flares.
So, making some guesses.......
Diameter of the parachute was 11 Feet, IV may indicate the type of parachute, Heathcoat Co is the manufacturer of the parachute. JHTD identifies the factory, John Heathcoat, Tiverton, Devon. (J H T D) and 10 May 1940 is the date it was made.
The company still makes parachutes.
https://www.bbc.com/news/uk-england-devon-64393066