Thanks Bastosako and Swampyjunior for confirming that and clearing up the confusion!
The reason why I was confused was because I checked online by clicking "EZ Search Parts Lookup" at www.arcticcat.com
and under the "Wiring Harness Assembly" for my model year, it stated the exact opposite (left is starter and right is battery)!! So obviously there is an error with the online parts catalog.
So I got it now. It's B for battery and M for Motor - the marks on the relay. That also means left post to battery and right post to starter motor.