We use an attractive oval gold label with our logo on it for various purposes. It has powerful adhesive on it and is difficult to remove once placed on a surface. After our wooden hangers kept departing with the guests, I began to affix one of the pretty labels to the thick part of the hanger, just under the hook that goes over the closet rods. I figured at least when the hanger reaches their closet, the guests will think about us each time they see it. Sure enough, several guests sent us emails that they realized that they had our hanger when they unpacked. One offered to mail it back to us (which would've cost more that a bunch of hangers since we now can find them reasonably priced.) We have jokingly told each of them that our inn policies required each guest with our hangers to personally return to the inn on at least a three night stay to return the hanger. And then we tell them to please keep the hanger, with our blessings.
We figure each person with one of our personalized hangers is a volunteer member of our marketing committee - even if the marketing is just to their family. And price isn't a huge issue when replacing the hangers. It is more of an issue to just go out and get the hangers. We started our bed and breakfast 6 years ago and learned along the way. Now, when we spot the hangers during our regular shopping, we simply add a box now and then to our storage supply for future use. Some of the organizations we are members of list wooden hangers in their criteria for inspections. While plastic ones won't flunk since points taken off are few, wooden ones are preferred.