12.E.6.b reads

A reserve pilot on RAP who has been called out for a flight
assignment ending that same day may also utilize this method
for release, but must also check his HI6 to determine his status
(returned to RAP or released to rest; the default is “released to
rest” if no HI6 is received).

Hence the requirement to check your hi6

PS Even with my lengthy tenure on the CRJ I've never seen that. Which is not to say that doesn't exist