Was taking the originator out of CHS to PHL last week, as I was doing my walk around, they were also boarding a CR2 to LGA across the ramp. Several passengers walked out of the ramp level door and immediately headed towards the stairs up to the jetway attached to the PHL flight. They were subconciously looking for the airplane with the jetway, despite the elevator ride they took down to the ramp from the terminal with the jetway doors. It took a good 60 seconds of me pointing at the CRJ for them to understand that it was the flight to LGA, not my 175.