I was thinking the same thing as I drove at 70+ (with my radar detector). "Well officer, I'm just a dumb Arizona boy and I didn't see where it said PICK-UP TRUCKS on that sign sir. " and then I could wait for the "Sign here. It's not an admission of guilt... . just a promise to appear in court. "
I did notice some different signs on I-8 east of SD that clarified by saying "all vehicles with trailers" instead of the normal "autos" and "trucks". That's the first time I've seen those. I think it was just before you start climbing up the mountain eastbound into InKoPah. I drove to Sacramento a few weeks before . Ever try to drive 1,800 miles at 55 MPH? Especially between Palm Springs and Blythe or between LA and Sacramento. Holy smokes! I couldn't wait to cross back into AZ so I could stop watching my rear-view mirror for the red and blue revenue collection lights. Man, I love California and vacation there every year, but I hate that stupid speed limit.
Maybe I should write a letter to the Governator and get him to fix this.