SR600 stands for Super Randonée. These are permanent routes approved and homologated by the Audax Club Parisien according to the SR rules.
You can read more about this here: audax-club-parisien.com/EN/421.html
To do a Super Randonée in British Columbia, you must be a member, and have filled out an event waiver. When you contact the route organizer, they will ask you to do these steps before permitting the ride of the route.
There is also a $6 fee the organizer will collect. In return you will receive a control card and a frame badge. This fee does not include postage of the items, should that be required.