In most BASICs I have seen, $ is standard for HEX, % for binary, 0 for octal and # for explicit decimal (in case the number has a leading 0, it doesn't get confused with octal).
255 ;decimal
#255 ;decimal
%11111111 ;binary
0377 ;octal
$FF ;hex
255 ;decimal
#255 ;decimal
%11111111 ;binary
0377 ;octal
$FF ;hex