Unfortunately, it doesn’t appear to be fixed in SU9:
If you type [ ; (without the space between the ‘1’ and the ‘;’) the forum changes this to [ so it appears the hashtag is simply the ‘code’ for the square brackets which appear.
Quite why TUI’s callsign (which should be TOMJET) is “Tui Air[52]” is anyone’s guess, but I assume it’s a simple typing error in the sim’s database of airline callsigns.