And why checked flags on an Autocross bus? Have they started using checked flags to indicate the end of a run?
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Why not use checkered flags? SCCA uses "Checkered Flag" to post obituaries, Chevrolet used checkered flags to denote certain special engine displacements and they still use checkered flags on their chest-hair wig and Viagra specialty car (Corvette).

I didn't check the previous postings but instead of converting a passenger bus to tow, I've encountered several folks that use retired ambulances as tow vehicles. One friend retained most all of the ambulance equipment including the power inverters, air-conditioning and "mood lighting" - very nice package complete with a Ford Powerpoker so it isn't completely gutless when towing.