Characters following the one-char operator are limited to the usual identifier characters.
Probably, the same character used as operator should be used in subroutines prototypes to allow for compile time optimizations. From then on symbols are actually treated like numbers, so comparisons are faster. They should be used to hold package names, method names and so on. A symbol scalar could be a read-only scalar with both the string and integer properties set. GLib's GQuarks and Xlib's Atoms for implementations.