Whats the easiest and surest way of telling if a frame has been tweaked in an accident?

As you ride on the crown (top) of the centermost lane of a straight stretch of road at normal road speeds, take your hands off the handlebars (hover them right over it of course) and see if your front end runs off to one side.  

Road forces say your front and rear wheel must track perfectly parallel to each other, so adjusting the rear wheel forces the correction up to the front wheel.   You adjust the alignment bolts on the rear wheel as if you were adjusting for the front wheel's errors.

Yes, you can "adjust" the tracking back to perfect (recover for some frame tweeking) simply by adjusting the error away by adjusting your rear wheel as if it were the front wheel.   You know you have succeeded when you can pass the "hands off test" and you can effectively steer the bike by the slightest shifts in your body's center of gravity.

I have a known warped bike that tracks correctly (ask the Dragon boys about it) and runs as fast or faster than any bike on the East Coast (that has ever come to the dragon anyway).

You can fix your bike if you want to ....

Just be aware that it will take some time for you to regain your confidence in the bike -- it was damaged and your mind knows that and you will be a little skittery for a while.

Stand the bike up as vertical as possible and point the front wheel straight ahead.  Sight from front to back (and vice versa) and see if one wheel is leaning with respect to the other.