Roberts made the gesture after celebrating Andrew Deaner's 90th minute strike, which looked to have sealed a 2-0 win for the Rebels. And, if league officials pick up on Roberts' actions, he could be in trouble with them.
On the field, Roberts faced more problems as his side threw away a two-goal lead in stoppage time. Slough were the better of the two sides and deservedly took the lead after 52 minutes through striker Brian Hammett.
And Deaner's superb late lob over Enfield keeper Andy Pape looked to have secured three points against Enfield, who had already been reduced to 10 men.
But Roberts' celebrations were cut short as Enfield ruined the Wexham Park party. With few stoppages in the game, the Rebels fans continued to celebrate what they thought was, at that stage, a certain victory, even when Enfield's Steve Terry converted, from what appeared to be an offside position, after five minutes of injury time.
But, astonishingly, the referee played 10 minutes of stoppage time. Pape joined the visitors' attack on numerous occasions at set-pieces and, in the end, the late pressure told.
Mark Bentley rose above the Slough defenders to nod home Darren Allan's superb free-kick and earn his side a valuable away point.
Enfield Line up
Pape, Annon, Naylor, G Cooper, Terry, Jones, Penn (sub: Deadman, 60), Bentley, Darlington, Richardson (sub: Dunwell, 72), S Cooper. Sub not used: Protheroe.