shove a stick or something into the exhaust, if it is stopped then there is a spark arrester inside. if the stick is not stopped and continues up the pipe, then no spark arrester.
Look around, you can buy bolt on spark arresters, i think they are pretty nasty lookin, but they do the job.
Im going to silver lake this friday - sunday. with my pc pipes and silencers, ive heard they run 95-96 dB, i better get in.