Yasin, who was born in London to Moroccan parents, was with Barnet and Aldershot Town in his youth career.
The attacker, who turned 23 on Friday, started his senior career in non-league and played for Farnborough and Lewes.
Following trials with several Premier League clubs, he eventually joined Newcastle United in 2016 and played in two FA Cup games for them. Ben El-Mhanni has recently been on trial with Championship side Brentford, and has been training with the Iron for the last couple of weeks.
He has been handed the number 19 shirt.
