Airspace on Sectional North of Boston

Can anyone tell me about the airspace marked on the New York
North Sectional 30 nm north of Boston. It's a circle of 30
nm radius marked with a heavy blue dashed line (sort of like
Class D, but heavier) and appears to surround P-67, the
Kennebunkport ex-president's abode. All color inside the
circle is removed from the sectional inside that area. I
don't see aything about that heavy dashed blue marking on
the sectional legend.

I'm guessing that it is the limit of the TFR expansion when
the president visits, but where does it describe this type
of marking for the sectional? Is there a similar marking
for the Texas presidential home? Any others? Have I got
this right? Other than a call to flight service (and
avoiding P-67) do I need to pay any particular attention to
this marked area?