The first thing you need to know is whether it is a high pitch or low pitch horn.  If it has "high pitch" or "H" engraved near the serial number it is not tuned to modern standards and its value is approximately zero.  If it has "low pitch" or "L" it is playable with modern instruments.  

The second thing you need to know is what type of saxophone it is, alto, c-melody, or tenor.  If the body tube is around 30" long it is a tenor.  If its around 25" long it's a c-melody.  If its less than 25" long it's an alto.

The third thing you need to know is its playing condition.  Have it looked at and tested by someone who knows saxophones, and get an estimate of what it would take to get it in top playing condition.  If it needs a lot of work it could exceed the value of the horn.

It's a nickel plated stencil (distributor/retailer branded) horn from the 1920s.  Yours looks like it was made by Martin because of the style of ring at the bow seams and the beveled toneholes.  Stencil horns generally are not worth a whole lot, but they can be good horns.  Martin stencils are a little more sought after than their contemporaries.  

Check closed listings of comparable Martin Perfacktones on eBay to get an idea of seller prices.