Delta is offering 40,000 bonus miles if you sign up for an American Express card by April 31, 2017. Here are the details:

Get 40,000 bonus miles after you use your new Card to make $1,000 in purchases within the first 3 months and a $50 statement credit after you make a Delta purchase with your new Card within the first 3 months^†.

Disclosure: I earn 5,000 bonus miles for each new card member.