If it's approximately 7" long, it appears to be a lock bar, that's used to lock the clutch basket and compensating sprocket from turning, on a 4-5 speed Harley Davidson bug twin motorcycle.
Goes between the chain teeth on the clutch basket and compensating sprocket. Bike is placed in gear so...
Plastic contains resins that can damage glass if rubbed over it. However, more likely, is the grit and winter dirt on the windshield that is stuck, and now scraped against the glass with the plastic scraper.
Either way: I hate winter.
I bought a fluted, heavy rubber mat off the internet. It was $325, but it's over 10 years old and has been exposed to abuse as a work surface, car parked on it and a motorcycle jack/lift. Hasn't missed a beat. Mine is 9x20. I see the price has gone up.
In the winter, I simply street-broom...