Technically, it didn't look like a ram’s horn, but rather a gazelle’s horn. (Either one is sufficient to use on Rosh Hashanah.) Since Jon Stewart is a producer for The Colbert Report, I think he just borrowed the shofar that Stephen Colbert used to sign off at the end of his show back in 2009.
I wonder what it would take for Jon Stewart and Stephen Colbert to come to my synagogue on Rosh Hashanah for a shofar duet?
Seeing Jon Stewart (Jewish) and Stephen Colbert (not-so-much) blowing the shofar got me thinking about Jewish rituals in which other celebrities have engaged. Here are a few that I was able to dig up:
Howie Mandell putting on tefillin
The Bob Dylan Tefillin
The Beastie Boys Playing Dreidel on Hanukkah
George Costanza, I mean Jason Alexander, Giving a Sermon in Synagogue
Ryan Gosling Leading Prayers (He looks like Eminem here!)
Leonard Nimoy Duchenen (Blessing the Congregation)
Krusty the Klown Reading Torah
Rabbi Ben Stiller Teaching Torah
Darth Vader Waving the Lulav