A better way to deal with this, however, is instead of slapping a sticker on someone's property, get custom-made brown paper bags with your logo on them, and put the growler in that after filling. It's a fun image, you get the branding, and the customer doesn't have the annoyance of either not having a growler filled or having a sticker put on his glassware. It's like this: http://revbrew.com/store/product/5001 except in a paper bag.
Or a pre-printed cardstock ring that is placed around the neck of the growler, like those around the bung of a Sanke keg.
I understand branding for sure, but the craft industry also has an image of working together and you don't want to appear like the only grouchy kodger who won't play along. Growlers are also marketed by many as a green alternative to disposable bottles, but forcing them to buy a new one is counter to that. And many customers do want, do not have the space, or do not want to spend the money on more growlers and you'll loose those sales.