Last month, I. Marlene King, aka in real life -A, tweeted that the girls were filming a new intro and that all of them would get a turn to SHHH this time. Today, E! released a behind the scenes video of the girls filming said intro, which in fact includes all of them doing the SHHH bit, and they also released the actual opening that shows Canadian Princess Shay Mitchell doing the SHHH at the end.
Because of the way Marlene's tweet was worded, and also because of the BTS video, rumor has it that they will be alternating between the girls doing the SHHH sign every week.
You can watch the BTS video H E R E and the complete opening H E R E
sources: 1, 2, 3, 4 + my words