Crazygal, what's the station name? How did you restore the sign?
As Cowford suggests, the value of the sign is directly related to (1) the name of the station, and (2) condition. Major resorts, notable junctions, most cities, branch line terminals will bring hundreds. East Somerville or Hayes, not so much. I was present at two auctions about five years ago where the signs for Bretton Woods and Crawford Notch were sold. Price for BW was $710, CW almost $1000 IIRC.
PBM