I ran into the same situation in January ... I had a hat with a protest slogan on it (written in Arabic) in my bag as I was leaving through Ben Gurion. Unfortunately, I was already flagged as a suspicious person due to stamps from Syria & Sudan in my passport, so I got searched very carefully. One security guy found the hat and asked me to translate it (I don't know if he could read Arabic or not). I said I couldn't read it and he seemed to accept that.
Ultimately, there was no problem, and I think the security guys were very polite. The key is to be friendly and respectful toward them -- they're just doing their jobs.
It did take me 3 hours to get through the security lines, though ... just be sure you get to the airport very early.