We tag the water shut offs inside the residence with a premade laminated tag. We also tag by there or by the controller with another tag for where the RPZ is, who has the RPZ over the winter (in place, with owner, with us) and what years we have serviced the site.
We tag the front of the controller also with another sticker with our name, website and phone number on it for people to call for service. Its like the garage door guys, name is everywhere.
For our backflow testing (we have another company do it because we can't... Stupid Illinois), they do a plastic sleeve that they slide the form into so a copy stays with the device at all times (as required).