The Windex works but I found the alcohol makes it dry pretty fast and especially on a hot day the sticker can get stuck in the wrong position. Use 1 tsp of dish soap to 16 oz spray bottle of water. As follows:
1) Measure to find center of window, cut a little piece of masking tape and put on roof line to mark it.
2) Trim the backing paper close to the bottom of the S and the N (for measuring)
3) Dont remove any backing yet! Place the decal, center it and measure the ends at the S and the N from the roof to the bottom of the letter, now place another piece of masking tape on the windshield under each letter where you measured making sure both ends are even.
4) Now you have 3 referance points for placing the banner. Center and both ends.
5) Clean window with alchohol (windex works for this part)
6) Get someone to help you with this part, remove backing, dont let it curl up on itself.
7) Spray window with soapy solution, and lay down the banner in it's position, move it around until it's right with your marks, leaving top paper on for now, Oh and dont get top paper wet.
10) Step back 10 feet, look at it. Does it look right? If so use a squeegee and squeegee the water out from underneath the Banner.
11) Wait 3 hours to remove top paper, remove it slowy.
12) Wait 24 hours before washing the car.
13) Good Job! Get yourself a diet Pepsi!
