The advice given is that you should always remove any imprint of the mount from your windscreen and take your GPS with you. There are literally hundreds of carry cases available to fit in a pocket. All you need to do is search for your model eg Garmin Nuvi 3790T. They generally cost less than $20.
I just spotted a cheap, Chinese, padded hard case with free screen protector and stylus for under $10. It has room inside for storage of accessories and looks very smart. It even has the Garmin name on it.