Described as able to play on either flank with a turn of speed and an eye for goal, Brown (pictured) initially joins the Rocks on a one month`s loan.
Rocks` boss John Coventry has also signed French-born attacking midfielder Vincente Belho.
Belho started the season with some impressive performances for Essex Senior League side Waltham Forest.
Departing the FutureFuel Stadium is Femi Akinwande.
The striker, who had a loan spell with East Thurrock last season, signed this summer after being released by Colchester, but has only made the occasional appearance this season.