How to tag "Untitled" tracks

[DetlevD]

I have scanned this web page quickly ...
http://musicbrainz.org/doc/Style/Unknown_a...ose_track_title
... and cannot find something what shows into the direction as what you have said ...

@deckard

... According to their standard, the track field would look something like this: [album, part x] [untitled]

The MusicBrainz style proposal offers some insight how to handle a track, which is in the state of 'untitled or unknown or having data only', and recommends the usage of three common placeholders, one for each status.
[untitled] ... for track with intentionally no title.
[unknown] ... for track with currently unknown title;
[data track] ... for track with no audio content.
The square brackets are only used to make the special meaning of the words visible to the reader.

Note:
The Mp3tag Scripting Language uses the square brackets as a special operator resp. as an inline function.
If you need a square bracket as a literal, then you must enclose it in single quotation marks.
Example:
If the tag-field TRACK does not exist, then you will get following results ...

[%TRACK%] ==> '['%TRACK%']' ==> []

If the tag-field TRACK contains the number 13, then you will get following results ...

[%TRACK%] ==> 13 '['%TRACK%']' ==> [13]

@deckard

So I have a lot of tracks that are named "Untitled". Lots of electronic releases have songs marked as "Untitled" or "Instrumental" or "Interlude", etc. and there can be many with the same title in the same release. I am looking for a good solution to make these tracks unique so I don't have hundreds of tracks showing up with the same name in my player. ...

The file system is a special storage that only works with unique file names.
So you have the need to give each file an unique name.

There is a proposal how to create a filename automagically ...
Share your custom Actions

Because a filename is nothing but hollow words, the problem is not the filename per se.
In the tagging process the creation of the filename is the last task to do.
So you have first to fill some tag-fields with data, from which an unique file name can be created
(ARTIST, ALBUM, YEAR, TITLE, TRACK).

If you know or suspect that the current song got a title by its author, but you cannot get this title into your experience, then you may follow the MusicBrainz proposal and fill the tag-field TITLE with the value '[unknown]'.

Beside to the foregoing, there is another possibility to make a filename unique by using a 'globally unique identifier (GUID)'.

DD.20121020.2040.CEST