Encouraging beginner scuba divers (and any scuba divers)
to drag their masks under their chins when they surface
is patently dangerous. In that mode, surfaced divers cannot
use their snorkels or their regulators very comfortably for
their swim to shore or the boat. One need only try this to
have the point proven.
I've been chartering around Cape Ann, MA on weekends
  and holidays for 32 years. We have to pull these misguided
  people with their masks around their necks to the side of
  the boat and "rescue" and "scold" them. They surface from
  a dive, drag the mask down to clutter under the chin, and
  snort and cough their way back. They say, "My instructor
  told me to." Invariably, that instructor is from PADI. Really
  bad business.
Surfacing divers must keep their masks on their faces
  while using either their snorkels or their second stages to
  maneuver to their destinations. My campaign, using our
  monthly newsletters to New England dive shops, may be
  bearing fruit. In March, at the Beneath the Sea show in New
  York, I had to travel nearly the entire sideshow of exhibitor booths before coming across one poster that depicted scuba
  divers with their masks wrapped at their necks. It was at
  the SSI booth, and the eager novitiates manning the space
  were chattering away and handing out information sheets.
  When I got the attention of one of the people working the
  booth, I advised her that the hapless divers portrayed on
  the back-drop couldn't make use of the snorkels attached to
  their masks - - and those people in the picture had to have
  removed their regulator second-stages from their mouths to
  have dragged their masks to lodge under their chins. What I
  got in return was the "thousand-yard stare" common among
  beginner divers who've been taught a wrong thing to do
  and have then been set upon the rest of us to evangelize the
  dangerous drivel.
Only one booth out of several hundred had scuba so
  poorly represented in its decorations. As I said, our campaign
  might be working.
Fred Calhoun has been a certified scuba instructor since 1958, and
  has taught more than 1,000 Navy scuba divers, owned a dive store,
  written nine dive books and currently runs a charter boat. He has
  produced the Boston Scuba Show since 1967.