The ex-Blackpool FC player - who was just last month released from jail after being convicted of fraud - scored his side's third goal as Southend won 4-2 at Fleetwood.
Ranger, who found himself in hot water during a spell at Newcastle United in 2011 when he was photographed posing with a replica gun, celebrated by taking off his right boot and taking aim at the home fans.
Using it as a mock weapon, he appeared to mime shooting into the stand, much to the anger of the crowd - and many on social media.
The Southend striker, 26, was playing in just his fourth game of the season, having had his electronic tag removed on Friday.
He fired home from the penalty spot in the 45th minute of the match at Highbury after he was ruled to have been felled by Nathan Pond in the box.
But it was his elaborate celebrations afterwards that angered the home faithful with a machine gun-style gesture similar to Robbie Keane's famous goal celebration.
The removal of his electronic tag and the lifting of a 7pm curfew following a 10-week stint in jail for online fraud allowed Ranger to make his return to the Fylde coast for the Saturday's League One clash.
Twitter user Baz Hay described Ranger's actions as a 'disgrace', adding: "I wonder how the FA police these lower leagues? Nile Ranger simulating gunning down the Fleetwood fans with his footy boot."
Martin Crane added: "Ranger's celebration was disgusting."
Ranger played for Blackpool from 2014 to 2016, making 14 appearances.