Mohammad,
Macros should not be identified using the $:/tags/macro tag because someone may want to store a macro an include it when required rather than make it global. If they remove the tag is is not longer considered a macro?
If the existing syntax field was altered to macro-syntax you could search for tiddlers with a macro-syntax field prefix, however sometimes there is by nature more than one usable macro in a single tiddler. For example a submacro that can be used in its own right, this would not work. This is why I favored a field macro-macroname containing the syntax, thus one tiddler can have more than one macro and the description can be generalised a little.
Regards
Tony