People from this region are known for "swallowing" their "Ls." To others, this is a very distinctive sound.
For example, to an outsider, when a person with the local accent says "Philadelphia," it sounds like "Phiwadewphia," not like a speech impediment, but just a quirk of pronunciation.
A speech therapist would tell you that it all has to do with where the tongue is placed when forming the "L."
There are, of course, regionalisms as well, but these are more like terms and not pronunciations. That "L" is the giveaway.
When I was a kid, we moved to PA from the NYC area, and everyone teased my about my NY accent. Now that I have lived in CA for many years, when I come home to PA for a visit, I hear the PA accent very strongly, you can be sure.