It's impossible to drive a major highway in northern New Jersey without noticing their presence. On the biggest buildings, the most prominent overpasses and always proudly visible are the graffiti tags "PK" and "KID."

They tend to pop up in the most astonishing places. While a lot of spray paint tagging remains confined to the back of box trucks or underneath bridges, the PK KID tags are always done in mind-blowingly difficult areas to reach, making it seem just as likely to be done by Spiderman as by a common, paint-wielding vandal.

What little there is to known about the source of these tags remains shrouded in mystery, but among the various versions of the urban legend there run a few similarities. The generally accepted premise is this: PK and KID are the monickers of two highly-respected, longtime street artists who use repelling, climbing ropes and other techniques to tag where few would dare.

From there, things get confusing and sometimes downright weird.

One story alleges that PK Kid is a single person, an East Los Angeles native named Diego Rivera who was a preacher's son (hence, "PK"). The story goes that Rivera began tagging on the turf of a powerful Mexican gang and his family moved to New Jersey to escape their reach. It is believed that he works as an appliance salesman somewhere in North Jersey.

Flickr user ELLLLL

Several versions of the story say that PK is a native of Staten Island, possibly even a New York City sanitation worker, though they are unclear if KID is a second individual.

Others maintain that the original PK and/or KID are retired. Noting differences in the letter style of older tags versus more recent additions, some believe that there are any number of impersonators using the PK and KID tags.

Due to the criminal nature of their acts, graffiti taggers are notoriously secretive and very little is known of the two to this day, though recently a growing number of "Free PK" tags can be seen along NJ roadways. Chatter on internet forums and comment sections suggests that one or both of them may have been arrested.

Check out the video below to see many of PK and KID's death-defying tags. Warning: the song contains explicit language.