Determining if the layer link is turned on or off

If you are in CS6 EXTENDED, where AM was still limited you can use this script (however it works in higher versions too):

$.level = 0; function sTT(v) {return stringIDToTypeID(v)}
function layer(v1, v2){
     try{
          (ref = new ActionReference()).putIndex(l = sTT('layer'), 0)
          if (((iN = isNaN(v1)) && v2) || !iN && !v2 && v1 != null) {
               executeActionGet(ref).getBoolean(sTT('background'))
          }
     }
     catch (err) {v1++}
     nu = v1 != undefined, eval("(ref = new ActionReference()).put" +
     (nu ? (iN ? "Name" : (v2 ? "Identifier" : "Index")) : "Enumerated") +
     "(l, " + (nu ? "v1" : "sTT('ordinal'), sTT('targetEnum')") + ")")
     if ((dsc = executeActionGet(ref)).hasKey(sTT('linkedLayerIDs'))) {
          with(psd = new PhotoshopSaveOptions()) {
               layers = !(spotColors = alphaChannels =
               embedColorProfile = annotations = false)
          }
          activeDocument.saveAs(fle = File('~/desktop/.psd'), psd, true)
          var m, lnk = dsc.getInteger(sTT('itemIndex')); (function() {
               fle.encoding = 'binary', fle.open('r'); var r = fle.read()
               index = r.indexOf('8BIM\x040'), fle.seek(index + 10)
               function bin(v) {return v * fle.readch().charCodeAt()}
               var d = fle.read(bin(256) + bin(1)), re = /\x00/g
               while(re.exec(d)) if (m = re.lastIndex == lnk) {break}
               fle.close(), fle.remove(); return m // DLL index
          })()
     }
     return Boolean(!m)
}

Examples how to use layer()​:

layer()     /     active layer

layer('layer 1')     /     layer 1

layer(1, true)     /     identifier 1

layer(0)     /     index 1 or background