It would be really useful to have a new filter option to filter out all cards that are signed.

I would suggest also adding "Is X" filters for any condition you can set on the card.

As far as I can tell, the following are missing filter options

"Is Signed"
"Is Artist Proof"
"Is Altered Art"
"Is Misprint"

I could definitely use the "Is Signed" filter to help me determine which card printings are actually in decks, since DeckBox still does not allow me to specific exactly which printing a constructed deck is actually using.