Car front windshield glue how to erase

 We all know that there are some signs will be posted on the windshield of the car in front of these flags insurance flag, green flag, inspection sticker, these signs affixed to the front of the car conducive to the view of the traffic police, the traffic police do not have a vehicle to gocheck to find the owner. This is relatively easy, these signs are not posts will be liable to a fine, but after the increase of the age of the vehicle, the flag will be more and more impossible to signs posted up, this will obstruct their view, hinder the car. Need to clear sign of expired, those behind the flag stick with glue, easy to erase, how can it thoroughly clean it?
Can with a toothbrush or cloth sticking point cleaner accidently erased with alcohol, alcoholic sticky cloth, erase with a rag. Then use the knife to gently scrape glue, be careful not to scratch the glass. Clear I glue in many ways, but need careful, cautious, the glass itself is relatively fragile and easily scratched, so the best wound with a cloth to erase, and try not to use the weapon, in order to avoid damage to the glass repairer.