Plastic Velcro (like Capt. Rich) attached to the WindVest crossbar - snap the ipass on or off and barely notice the remaining clear velcro when the ipass is removed.
Illinois roads and it hasn't come off - must be very strong velcro!
I've got mine in the exact spot as the top photo. I also spray painted the entire tag a flat-black color, so you can barely tell it's there. Just make sure to tape off the 'barcode' sticker on it, if it has one.
I nailed a deer at 50mph and it didn't pop off the windshield.
Guys, guys, guys. We have the perfect place for the transponders!
A small strip of black Velcro on either side of the gas cap, invisible when transponder is not needed. When transponder is mounted, is within easy reach and does not suffer from wind buffetting.