The tall striker joined the newly promoted side following his release from recently relegated Oxford United - the club he left the Shots to join last season.
Sills began his career as a trainee with Millwall, but made his name as a prolific non-league goal-scorer with Basingstoke, Kingstonian and the Shots where he netted 43 times in 89 starts.
Sills joined struggling Oxford United in January 2006 however, his disappointing strike-rate of just the one goal in nine starts, combined with the U's relegation in May, led to his departure.