ALL electronics should be marked clearly on all sides of the package "FRAGILE - GLASS CONTENTS - DO NOT DROP"
When the drivers see "GLASS" they take notice. Otherwise for all they know it is a book or t-shirt, etc.
I really don't think they care about fragile stickers. I've never placed any stock in "fragile" stickers, and never used them unless they were already on a reused box. Glass has to be properly packed to be unphased by a modest drop, or any claim will be rejected on that basis, regardless of stickers.
What I have been told is that (maybe) they take more care with packages insured over a threshold of about $900 - 1000.