Imported from http://bugs.musicbrainz.org/ticket/801
There is probably a reason why these weren't added while aliases for works were, but if there's not, they could be useful. Examples from the original Trac:
http://musicbrainz.org/showalbum.html?albumid=126435 is currently entered as "π (Pi)". Adding it as π with an alias of Pi would be a better solution IMHO.
http://musicbrainz.org/album/417d6a24-cf07-47c1-bd0a-639c8e16be7f.html Track 9 is called Infinity. It's listed on the album as ∞ (symbol for infinity), but adding aliases of "Infinity" and "nieskończoność" (Polish for infinity, commonly used since the band is Polish) would also be good.
On http://musicbrainz.org/album/bac7709a-507b-4e57-bc04-988180c9bf18.html , tracks 1, 3, 26 and 29 have symbolic titles on the cover tracklisting. ASCII representations of these are common, ( and ) for half circles,  for square, () for Circle. If unicode circles, half circles and square exist, these could be used also, such as ○ for Circle, □ for Square. Aliases of Square for , Circle for (), Open for (, and Close for ) would be useful.