(Symbol Type): Avoid makeinfo warning about colons in indices.

lispref/objects.texi

@@ -530,7 +530,9 @@ char-to-string      ; @r{A symbol named @samp{char-to-string}.}
 @end group
 @end example
 
-@cindex @samp{#:} read syntax
+@c This uses ``colon'' instead of a literal `:' because Info cannot
+@c cope with a `:' in a menu
+@cindex @samp{#@var{colon}} read syntax
   Normally the Lisp reader interns all symbols (@pxref{Creating
 Symbols}).  To prevent interning, you can write @samp{#:} before the
 name of the symbol.