It's always good to ask.

Abandoned building--who would you ask? No one to ask.

Keep in mind--if you don't already know this--that rose seeds of cultivated varieties will not reproduce the parent. They may bear a resemblance to the parent, or they may not.

If there is a way to find the owner or inhabitant, I ask. If it's apparent the place is abandoned, I will purloin seeds. If it's an old homestead or cemetery where determining ownership is quite involved, particularly if it's out of my normal area so returning is difficult or expensive, I will "liberate" cuttings/hips/seeds. My prime directive in all of the cases is "do no harm". I want the plants to be as good, if not better, after I leave them. That applies even in cases where I have been given free reign to collect cuttings/bud wood from someone's garden. Kim

What Kim Said:

Someone asked me once if I asked permission before "liberating" cuttings from a truly un-cared-for cemetery.

The answer probably should have been, that determined to "do no harm" I've found trying to find someone to ask to be futile.

What I actually SAID was:
"But everyone there is dead."

I've taken rose hips from places like my doctor's office, shopping malls and motels. I'm careful not to damage the plants in the process, of course, but really the mow & blow guys are just going to hedge trim them off anyway. As for neighbor's roses I always ask first. 99% of the time their thrilled I wanted some of their roses! So for me I'd be likely to take some when they were ripe since you know the place is abandoned anyway. As long as you don't damage the plant no one will probably miss a few hips. .

Thank you very much, guys. :D