A Brooklyn teenager who caused an explosion and snarled subway service when he threw a metal sign onto the tracks will be under scrutiny in a court program now that he's out of jail, authorities said.

He was also known for dangerous rail pranks in a transit vandal group called the "Subway Conquestors."

Keyshawn Brown, the 16-year-old son of an MTA conductor, pleaded guilty to two counts of criminal mischief and was released on July 30, correction and court records show.

He tossed a metal MTA sign onto the tracks at the Nostrand Avenue station in April -- which made a loud boom and created smoke when it was struck by a C train, court papers state. The incident was caught on video, which went viral.

Brown was also arrested earlier this year for allegedly attacking a transit enthusiast at an N train subway station in Brooklyn and hitting him in the back of his head with a metal pipe. He pleaded guilty to attempted assault, records show.

He and other 'Subway Conquestors' used Facebook to document underground antics that ranged from stealing signs to MTA keys-- as well as show off an array of subway-themed clothing.

Recently, Brown posted a message on his apparent Facebook page about R train subway surfing, with the hash tags "#ThrowbackThursday" and "#MTAPirates."

"Since his social media activity was instrumental in leading to his arrest, you can be certain that the NYPD Transit Bureau will be keeping an eye on him," said MTA spokeswoman Amanda Kwan.

A Brooklyn district attorney spokesman said Brown is being supervised through a court-mandated program while on probation.

The Transport Workers Union Local 100, which represents MTA workers, said they would like to see Brown banned from all transit property because he endangers workers and riders.

"Subway saboteurs should not be trifled with, we are all due to the confined subway spaces often unable to escape their nefarious acts," said Kevin Harrington, a vice president who represents train operators.

"He is not a harmless, laughable, criminal prankster, but someone who uses 600 volts at 80 amps of power as part of his crimes. He's a young man and should not have his future destroyed, but his endangering behavior has to be addressed as well."

Lawyers for Brown could not be reached for comment.