Probably short for "Ain't it so?" Common in northeastern Wisconsin a generation ago. Added at end of sentence as a question.
It's hot today, inso?
I've always heard it used at the end of a sentence.
Tommy sure looks great,inso?
If I bring the chips and rolls, you can bring the paper plates, napkins,and silverware, inso?
irrelevant guy spending all his time on eating 'junglevrål' without offering his friend any!
<kippe> nice, junglevrål! can I taste?
<inso> no, these junglevrål are too important to be eaten.
<kippe> oh, okay.
1 hour later..
<kippe> what the' !? were are all the junglevrål?
<inso> fanbahaag! >:D I ate them, and alot of my important friends had some too!
<kippe> *sigh* :(