PA state police patrol this area. They hide very well and use instant on K band radar. They usually try to pop you for speeding.
If they catch you driving on 15 south after the maryland border, near or after gettysburg, they may ask you to fill out a "consent to search" form or ask you to consent to a search.
They are looking for illegal fireworks or alcohol purchased in maryland (it is illegal to buy alcohol out of state and bring it into PA). Obviously, they will also look for any other contraband.
I recommend putting any alcohol/other things out of plain view (in the trunk) and not consenting to any searches whether you have anything or not. If you do have an out of state bottle of wine (god forbid!), then I'd suggest driving the speed limit.
You can read about my experience with the PSP here: