The motto of The RAF is: Per Ardua ad Astra
"Through Adversity/Struggles to the Stars."
So in this case 'RAF stars' = Astra; 500 in Roman numerals = "D" - the definition is 'Indicator of future.' Hope this helps.
I think this is simply the sound of 'tray (a carrier)' and its origin/first letter 'T' - giving 'Trait.'