Bought a similar CO2 bottle at a garage sale- took it in to get it filled- the guy at the gas outfit showed me a stamping on the bottom- "Property of So and So Bottling Co."
Gas guy said their deal with the bottling co. was that if I would just leave the bottle for return to them, that would be that, and company would not ask who had it. But if I insisted on keeping it, he would report it to the company, and they would prosecute for theft. I asked how he would know who to report, he smiled and said, "Well, I guess there are some drawbacks to living in a small town, Mr. xxxx."
Since he had my name right, and because the manager of the bottling Co. was a friend of mine, I decided I was in a hole, and better stop digging.
I did ask if they really did prosecute, he smiled again and said "Dunno. So far, everybody has taken Plan A, like you did."