If this is like all the other etching companies out there, then the "product" is the insurance policy. I highly doubt that a random number etched in the glass prevents thefts. After all, vehicles already have a number of 17 digit codes on them already and that doesn't seem to stop thefts.
I did look at the sherlock.ca site. Although in French I was able to see the APA logo. This endorsement must mean this etching is good, right?
edit:
After finding the "English" button, it looks like they don't sell any insurance. They just sell the marking. Interestingly, they mark much more than just glass. They also mark the wheels, lights and underhood parts. And if you don't want your expensive alloys to be permanently marked you are out of luck - they say they either mark everything or nothing.
Based on the OP's post, this excerpt from the site may be of interest:
The $259 published retail price allows a fair return to the dealer, and Sherlock does not tolerate a dealer selling its product at a higher than suggested retail price; in fact, APA learned that Sherlock has actually ordered dealers to refund overcharges to consumers.
