Back in 1982 Digital Research released DR PalmDOS which ran on Palm personal digital assistants.  When you used a PCMCIA card for storage, instead of adding a drive letter, it added a drive number - 0:, 1:, 2:. Today, even with Windows 7, non-alphabetic characters can be used, including  $ [ ] ` { } etc.  But some characters are just too special and cannot be used: % & ^ = | \ " ; , /..

The subst command is the only way I could find for using these, though.  This could be handy for a system where you are connecting removable media and you would have trouble knowing which drive letters would be available.  For example: [more]

subst 1: "C:\Documents and Settings\username\My Documents"

subst *: "C:\Documents and Settings\username\My Documents"

Unfortunately, the regular Explorer windows cannot handle these "special" drive designations, but they can be used from the command line.