--53--
Don't guess at character distribution.
Here's how they were used in the following 5 real-world examples.
CnetBugs.txt               84446 ----rwed 24-Jul-92 03:12:09
 : Cnet HQs base #7 `Bug reports' 23Jun92-23Jul92
BBSads.txt                 88658 ----rwed 23-Jul-92 08:23:12
 : C-net HQ's BBS ads msg base 23Jun92-22Jul92
BBStext                    45633 ----rwed 22-Jul-92 06:27:37
 : C-net BBStext file
Usenet.txt                227710 ----rwed 21-Jul-92 06:25:42
 : Amiga Usenet hardware msgs 14Jul92-20Jul92
Fido.txt                  140384 ----rwed 29-Mar-92 06:53:20
 : Amiga video Fidonet Echo msgs Apr92-May92
5 files - 1169 blocks - 586831 bytes

Count -f Cnet.txt,Usenet.txt,Fido.txt  -c ~!@#$%^&*()_+|\=-`{}][:"';<>?/., -C
Count v0.4, Jul 23 1992, (c)1992 Bill Beogelein

 `CnetBugs.txt' opened for input 
 Total chars: 0 
 `CnetBugs.txt' closed 
  !x226   	  "x106   	  #x4     	  $x4     	  %x3     
  &x13    	  'x209   	  (x355   	  )x367   	  *x21    
  +x3     	  ,x431   	  -x760   	  .x1226  	  /x121   
  :x1181  	  ;x16    	  <x19    	  =x205   	  >x90    
  ?x241   	  @x6     	  ^x150   	  _x15    	  {x4     
  |x28    	  }x4     	

 `BBSads.txt' opened for input 
 Total chars: 0 
 `BBSads.txt' closed 
  !x293   	  "x48    	  #x12    	  $x3     	  %x2     
  &x9     	  'x280   	  (x323   	  )x334   	  *x409   
  +x15    	  ,x389   	  -x1090  	  .x1845  	  /x876   
  :x1206  	  ;x642   	  <x117   	  =x56    	  >x119   
  ?x117   	  @x2     	  [x647   	  ]x14    	  ^x58    
  _x1108  	  `x14    	  {x2     	  |x207   	  }x2     

 `Cnet:BBStext' opened for input 
 Total chars: 45633 
 `Cnet:BBStext' closed 
  !x64    	  "x18    	  #x69    	  $x8     	  %x676   
  &x4     	  'x90    	  (x159   	  )x202   	  *x19    
  +x9     	  ,x197   	  -x224   	  .x856   	  /x47    
  :x557   	  ;x18    	  <x10    	  =x242   	  >x39    
  ?x180   	  @x12    	  [x140   	  \x2228  	  ]x135   
  ^x9     	  _x0     	  `x2     	  {x297   	  |x0     
  }x297   	  ~x0     	

 `Cnet.txt' opened for input 
 Total chars: 11236 
 `Cnet.txt' closed 
  !x5     	  "x72    	  #x1     	  $x108   	  %x44    
  &x31    	  'x14    	  (x53    	  )x44    	  *x55    
  +x14    	  ,x132   	  -x100   	  .x85    	  /x142   
  :x14    	  ;x15    	  <x36    	  =x2     	  >x5     
  ?x19    	  @x125   	  [x4     	  \x5     	  ]x5     
  ^x27    	  _x13    	  `x164   	  {x0     	  |x31    
  }x5     	  ~x9     	

 `Usenet.txt' opened for input 
 Total chars: 227710 
 `Usenet.txt' closed 
  !x503   	  "x195   	  #x481   	  $x105   	  %x18    
  &x43    	  'x613   	  (x751   	  )x809   	  *x1045  
  +x199   	  ,x1259  	  -x6554  	  .x4623  	  /x300   
  :x1477  	  ;x26    	  <x105   	  =x1120  	  >x1151  
  ?x489   	  @x1031  	  [x18    	  \x123   	  ]x16    
  ^x93    	  _x544   	  `x13    	  {x13    	  |x464   
  }x11    	  ~x167   	

 `Fido.txt' opened for input 
 Total chars: 140384 
 `Fido.txt' closed 
  !x165   	  "x473   	  #x174   	  $x29    	  %x3     
  &x21    	  'x461   	  (x568   	  )x576   	  *x261   
  +x23    	  ,x717   	  -x1449  	  .x1896  	  /x409   
  :x1808  	  ;x26    	  <x2     	  =x121   	  >x430   
  ?x151   	  @x26    	  [x19    	  \x4     	  ]x18    
  ^x3     	  _x32    	  `x1     	  {x0     	  |x0     
  }x0     	  ~x4     	

Looks like "{" and "}" are very little used chars in msgs.
{n2}
{c2}
{b3}

Also would look pretty good around the handful of MCI codes that
need both a 'start' and 'end' marker.
{#2pFiles:name}
{*0filename.txt}
{#0Rexx:file.rexx}
{#4c:CMD %1 %40}

But they are used very heavily in BBSTEXT, making them a VERY poor choice.
I'd leave this one at "\" instead of changing it now.
