If you like me have some stainless steel exhaust pipes on your motorcycle which have patches of dark color on them and wonder if there's a way to get them back to as-new condition... Stainless steel can discolor but it's possible to get it sparkling again. The quick way is to leave the exhaust in place, get some steel wool with some metal polish. Put a bit of polish on the steel wool and give the exhaust pipes a rub. It takes a bit of elbow grease but it'll bring them up nicely.
If you want to do a really impressive job, you'll have to take the exhaust system off. Running the engine to heat the studs makes them less likely to shear off. Once the exhaust has cooled, you can use increasingly fine grades of wet and dry paper to remove the surface contaminants and bring the exhaust to a mirror shine. The best and easiest way to finish the job rather than using the very finest wet and dry is a polishing mop. A white close stitch mop from the local DIY shop and some polish compound will bring it up beautifully when attached to an electric drill.
For those people with mild steel down pipes, the job's more involved – and more important to stop them rusting through. Ideally remove the whole system and rub thoroughly with a wire brush to get rid of the rust. Pay particular attention to the creases in the collector box. Then re-spray the whole thing with heat prof paint. Black is best but other colors are available if you like the look.