Any suggestions?

Razor blade and a lot of elbow grease.

"house brick"

heat gun...........

As much ammonia as you can stand.  Let it soak and it should come off fairly easy.

Quoted: Razor blade and a lot of elbow grease.

+1.  

Quoted: www.tintcenter.com/articles/bt_removal.html

Big +1, especially if you've got a rear defroster.  I read thru this, decided it was too much trouble, and tried to take it off with a razor.  Bad move.  That back window still had shit on it when I sold the car.  

Score the film with a razor blade then soak it
down with plain ole Windex ( Liquid not foam )
It doesnt dry as quickly as straight amonia .

Keep it wet for a half hour then use a razor scraper
to remove it . If it's a cheap film it will almost fall off .
While the better ones take more soaking and work
to remove .  Razor blades are cheap , so keep changing
them once they get gummed up . Because dull blades
will peel the film and leave the adhesive behind , making
twice as much work .

I get at least one vehicle a month that I have to remove
the tint on the drivers door glass because they get a ticket
for having it too dark .

There is a professional adhesive/sticker remover spray
but it’s pricey and stinks like shit , and doesnt work much
better then Windex .

Ask a tint place to quote you, I read a book while they sweated.

I can't remember how much they wanted, but it was a deal.