Any backflow that I have seen that has been tested, has had a tag on them. But that is only about 5 in the last 5 years. I used to put a tag on the shut off handles, so at least the H/O or tenant would know which handle to turn off in case of a freeze. But I got away from it.
I get tired of hand holding for all the customers. So many act like they are completely clueless and can't tie their own shoes.