According to this article on PageSix.com, Marg Helgenberger of CSI: Vegas, the cast members from Reno 911 and from Bones were among those gathered to protest on behalf of the WGA writers.

Crime show writers and stars were out in the Los Angeles rain this morning to deliver a message to the studios: you’re under arrest!
CSI’s Marg Helgenberger, bundled up in a coat and hat, stood on the back of a pick up truck and read the group’s “bill of indictment” against Hollywood big wigs. When some scribes in the back asked her to speak up, Marg joked, “And I’m supposed to be an actor!”
CSI, cbs, CSI las vegas, tv, Television

WOOP WOOP ! Go Marg Helgenberger ! she always puts up a fight for what she believes in and is a great influence to everyone !
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[...] Helgenberger is in total support of the writers’ strike, as I’ve reported previously. What you may not yet be aware of is the fact that her husband, Alan Rosenberg, as President of the [...]
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