On Dan and Dave's website you can Request an Autograph [Link]; they will take one card of their choosing, sign it, and mail it to you.

I requested one a few weeks ago and the postal worker delivered a small envelope today.

The front of the envelope had my address handwritten on it with a $1 US stamp.

The back had "Dan + Dave" on it:
User Image

Inside was my autographed card:
For those of you wondering, it's the ad card from the Smoke & Mirrors v4 deck.
User Image