According to the MTA Weekender:
F Coney Island-bound trains run via the M from Roosevelt Av to 47-50 Sts
Weekends, 11:15 PM Fri to 5 AM Mon, until Sep 8
Trains run express from Roosevelt Av to Queens Plaza.
No Coney Island-bound service at 21 St-Queensbridge, Roosevelt Island, Lexington Av/63 St and 57 St.
According to the Twitterverse:
@pianobarry @Rooseveltisland That sign is placed on the four stations that are bypassed. If you were in QB you would have to follow the sign
Ratso (@Okrick222) August 29, 2014