I find the idea of Rosh HaShanah cards a little odd; Rosh HaShanah is a nervewracking time, by the lights of Jewish tradition. Classically, some even fasted on Rosh HaShanah, although that is no longer in halachic vogue. It's the Day of Judgment, books of living and the dead, angels trembling... So why are we sending happy cards full of smiling faces to each other?
לו איישר חילי, I would abolish them.
(Except for this cute card I received: "How's your New Year going?" "Shofar, so good!" I really enjoyed that one, Ralph.)
On the other hand, Yom Kippur cards make a lot of sense. This is, per the gemara at the end of Taanis, one of the greatest days on the Jewish calendar. We should walk through the day with a big smile (except when whacking ourselves on the heart for our sins; then, a grimace may be permitted).
We are all unified, we pray together, what could be better (aside from a big burger with fries)?
I could even see a sort of fill-in-the-blank Yom Kippur card, customizable to request or grant forgiveness for anything you choose:
We have been thinking about the past year, and we regret some of the things we said and did. Specifically, we want to ask your forgiveness for:
(Here would be a big space for those who have a lot to list. Those who prefer not to list anything could draw a picture, or insert a family photograph.)
In contemplating the past year, we also recall some of the ___________ (intense adjective) things you did. Rest assured that we forgive you for those as well, even including:
(Again, feel to write as much or as little as you like.)
This coming year, we hope, will be a better one. Whether you are voting for the right candidate or the other one, whether you are making aliyah or joining American Friends of Peace Now, whether you are a fan of my team or any other, whether you are inviting me to your daughter’s Bat Mitzvah or not, whether you ___________________ or whether you ___________________, we pray that Gd will give all of us a happy and healthy new year.
Smile - it's Yom Kippur!
Perhaps Aish or NJOP will come up with one next year.
Until then: Have an easy and meaningful fast, צום קל ומועיל, and גמר חתימה טובה,