:laugh:
They are bytes values added to the end of the string, that cannot be added by normal typing. In this case a carriage return, a line feed and a terminating null character.
In C-type languages, this would be the equivalent of writing:
char* Hello = "Hello World!\n";
It is a good idea to declare these as mnemonics though, so you can use readable names instead of numbers:
Hello db "Hello World!", AS_CR, AS_LF, 0
(I probably wouldn't use AS_NULL for the zero, as it would most likely be a string terminator, rather than a character to display)