OK, this will suck if you have a lot of playlists, but try this:
Make a smart playlist where:
"Playlist" is "pick a playlist from the dropdown" +
"Playlist" is "pick a playlist from the dropdown" +
"Playlist" is "pick a playlist from the dropdown" +
"Playlist" is "pick a playlist from the dropdown" +
"Playlist" is "pick a playlist from the dropdown" +
...until all your playlists are included.
This would at least give you one big playlist made up of all the songs in all playlists.
Then, presumably you could shift-select them all, take "get info", and put something in the "grouping" field (assuming you're not using it already) like "playlist track".
You now have a "grouping" tag set for all tracks that appear on a playlist somewhere.