Symbols as label shorthands

Using symbol can help shortening length of label list in GMail's subject display.  One awareness of choosing a symbol is that it must be specifiable in search input-field: i.e., not becoming "-" or "%xx" in search formula (need verifying).

Label	Description / Usage
!?	For incoming problem/issue. However this is neither for question ([?] star) nor user incident ("@ users").
!!	Important
^	Caret: for filter: from:(bosses), as alternative to star marking.  This symbol indicates "above".
/	Slash: OK, done.
\	Backslash: moved and/or filed somewhere else: i.e., different thread/subject or outside GMail.
=	Equal sign: the mail has been assigned to (or handled by) someone else.  In most programming languages, "a = b" is recognised as assigning (copying value of) b to a -- or "substituting".
++	Selected active/ongoing conversation thread.  Any GMail subject can become thread.  But this is useful when we want to find back certain threads which should be updated regularly, such as periodic reporting, news updating.
--	Demoted: supposed to be processed somewhere or by someone else.  This can be complement to \ and =; whereas those labels imply known destination, this label doesn't define destination — just "anyway but not by myself".
0!	Zero: "No", skipped, missed, incompleted, failed, none to action/progress, too late.  Previously, 'X' was under consideration, but it seems ambiguous between no/cancel and yes/checked.  However, '0' can also look like 'O' for OK/ongoing, so better add '!'.

Remarks

• Slash/Backslash: These symbols are used in marking completion in checklist -- source of idea here.
• / and = are same usage as ".run" and ".taken", more explanation here.  However, \ may be considerably addition to ".taken" to differentiates between handled-by/assigned-to someone (=) vs moved/filed elsewhere (\).
• In April'10, GMail released lab feature "Nested Labels" which uses slash to create sub-label.  However, "/" label seems not effected from this implementation.
• Idea of ++ and -- is from C programming language.  They are "increment" and "decrement" operators respectively.