The 33-year-old has been training with the Iron for the past couple of weeks and joins up with another ex-Crawley player in experienced striker Lee Barnard.
Ashton began his career at Leicester City, making nine appearances, before moving on to Oxford United, where he played ninety-one games for the U's over three seasons.
He then spent a season with the sadly now defunct Rushden & Diamonds, making forty appearances, before signing for Stevenage in 2009.
In six years with Boro he featured in 192 games, before joining Crawley last summer.
He made thirty appearances for the Reds last season before his contract ran out at the end of the season.