Depends. I especially like a postmark and written info when it relates to the subject or to an event, like a little capsule of history. Like this PC:
The card shows Jim Jeffries sharpening a tool with three onlookers. The card is labeled "Rowardennan" which was the Jeffries training camp in Santa Cruz CA. It is initially postmarked in June 1910 and recites how "the big fellow is getting better every day sure thing."
Or this one, which is signed by HOFer Carlos Ortiz's manager and invites a boxing writer to an Ortiz fight in 1957:
Also makes it very hard to fake the item.
Finally, since the technical grade of the item is less than good when written on and postmarked, it also often means you can score the card on the cheap. Less money in each card means more cards for me!