If you have a bill of sale from the guy you bought it from, then you have a paper trail that leads through you to him. IF the quad ever does turn up as stolen, it will get traced back to you, but you then have proof that you at least purchased it, which will help.
If you do not have a bill of sale from the guy, then the trail ends with you unless they cops can track him down (quite unlikely). In this case, basically you are screwed. It sounds like you have always suspected that this was stolen, now you are paying the price.
'07 Can-Am Outlander 800 XT - Crutchfield stage I Extremes all around
'02 Eiger 5-speed / mudlites
Past bikes: '89 Warrior, '97 Warrior, '98 LT80, '94 King Quad 300, '84 LT50