How to determine if a voltage is regulated and rectified using AN8008 multimeter?
Puh, that's a multimeter, and not an oscilloscope. This might limit its usefulness for this purpose.
Anyway, you can try putting it into AC mode; where it reads a high AC voltage, you have ripples. That's not a very good measure, though, because it will neither detect strong fluctuations beyond the bandwidth of your measurement device, which will still interfere with your loads, nor will it allow assessment of what happens when you actually attach a load to that power rail, so it might detect things that don't matter.
In all honesty: on motorcycle wiring, unless you're already taking your voltage from within an electronic instrument, assume nothing is smooth. Nothing.
Instead, you'd want to add your own ESD-protected  voltage smoothing capacitors and a voltage regulator. There's not that much way around that.