Many words we all use in basic conversation were once or are still a trademarked brand name of one company or another. Sharpie, post-it, wite-out, band-aid—all of these are nouns that we use to refer any number of items: permanent markers, adhesive note paper, correction fluid, and self-adhesive bandage.
Of course if you go onto a web site or read a brochure from a competing company who produces one of these products under a different name you will see the generic name and not the brand name of the other company. Avery uses the term “permanent marker” for their line of Marks-A-Lot® indelible markers, but of course if you asked someone to hand you a sharpie and they gave you a Marks-A-Lot® marker you probably wouldn’t say “no, I wanted a Sharpie® brand marker.”
In spoken conversation we don’t have to interject trademark symbols or copyright lines, but when we use a company’s trademarked product name in print or on the web we give that company acknowledgment with a copyright line or a generic disclaimer stating that you do not claim their products and services to be your own. Part of my job is to find product names in copy that is being laid out by a designer and decide how to acknowledge the ownership of the product being named. A lot of the time we just use a footnote that says the product name doesn’t belong to the company producing the literature. Part of my QA process is helping companies protect their branding and legal claim to their product names.
Aside from the serious issue of losing their legal claim to their product name, I wouldn’t think that companies mind their product names being used generically—it means that they are so popular that everybody thinks that item is called whatever unique word they came up with, no matter who makes the product. How cool is that.