I put (Disc 1), (Disc 2) and so on, in the album name. sometimes im too lazy to separate discs so i leave them in one folder and put (2 Discs) in the album name.
At least this way i can separate them some day when i am bored.
i don't like using the disc # field because it doesn't account for parts or volumes.
i have many singles of the same name but of different parts so i use (Part 1), (Part 2), etc instead of disc numbers
you can also add more info after the disc number like Vol 1, Vol 2, Remastered, Deluxe, Japan Edition, Amazon Exclusive, Collectors, HD, Expanded, Reissue, Promo, etc
You can shorten these up too. Rm, Dlx, Amazon Exc, Coll, etc.
An example:
The Downward Spiral
The Downward Spiral (Disc 1 Rm)
The Downward Spiral (Disc 2 Rm)
The first one is the original release the second and third are the remastered reissue.