I've had my 2015 GT Premium with security package in the garage covered for 2 months. I pulled back the cover today, and none of the lights went on when I opened the door. I connected my trickle charger to the battery, and every few seconds the car makes some noises almost like the fuel pump is...
Try hot water (no soap) on a rag, hold it on the spot for 30 seconds or so to soften and then see if it wipes away with the rag. If it's stubborn, re-apply the hottest water you can stand and try wiping it away. Then wash with car wash soap and water.
Works on dried bug guts on the motorcycle