The Guild Signets (Boros, Dimir, Simic, etc.), added with Arena Anthology 1, are shown as "banned" in Timeless, hence Decks are treated as illegal in my deck collection.

The signets also dont show up in the Deck builder if Timeless is the selected formate.

Also cards that have a Dimir watermark (Watery Grave, also overs) show the Mirage Set Symbol as watermark.