How to use Javascript to detect a signed Acrobat document?

Here is the partial code for Step 8 (Javascript). The original code is in ilatics. My comments/questions are in bold.

// place labels
global.DoPlaceDocNumbers = app.trustedFunction(function(oOrigDoc) {
app.beginPriv();

// test whether the file is signed; if it is not, it can be labeled. Otherwise it is skipped.
if (oOrigDoc.securityHandler == null) <--I need this to test if document is signed or not. If it is not, then all steps in italics below should continue. I realize it is pointing to encryption and I am trying to integrate your code instead by adding:

var isSigned = false;

for (var i=0; i<this.numFields; i++) {

         var fname = this.getNthFieldName(i);

         var f = this.getField(fname);

         if (f==null) continue;

         if (f.type=="signature" && f.value!="") {isSigned = true; break;}

}

but no luck so far due to syntax errors.

{var oTrgDoc = oOrigDoc,
nPgStart,
nPgEnd,
nPgTrgStart,
cBkCol = ["T"];

/* set background color */
switch (global.DocNumAction.strBackgroundCol.toString()) {
case "Transparent":
cBkCol = ["T"];
break;
case "Yellow":
cBkCol = ["RGB", 1, 1, 0];
break;
case "Green":
cBkCol = ["RGB", 0, 1, 0];
break;
case "Blue":
cBkCol = ["RGB", 0, 0, 1];
break;
case "Grey":
cBkCol = ["RGB", .7, .7, .7];
break;
case "White":
cBkCol = ["RGB", 1, 1, 1]
}

/* set page range selection */
switch (global.DocNumAction.strPgRangeSel) {
case "rAll":
nPgTrgStart = nPgStart = 0,
nPgEnd = oOrigDoc.numPages - 1;
break;
case "rCur":
nPgTrgStart = nPgEnd = nPgStart = oOrigDoc.hidden ? 0 : oOrigDoc.pageNum;
break;
case "rFro":
nPgTrgStart = nPgStart = Number(global.DocNumAction.strStrtPg) - 1, nPgTrgStart > oOrigDoc.numPages - 1 &&
(nPgTrgStart = oOrigDoc.numPages - 1),
nPgEnd = Number(global.DocNumAction.strEndPg) - 1,
nPgEnd > oOrigDoc.numPages - 1 &&
(nPgEnd = oOrigDoc.numPages - 1)
}

/* process the selected page range */
for (var nNumPages = nPgEnd - nPgStart + 1,
nCurPgNum = nPgStart,
nPg = 0; nNumPages > nPg; nPg++, nCurPgNum++, nPgTrgStart++) {
var strExample = global.DocNumAction.strLabelPrefix;
global.DocNumAction.bIncludeDocNum &&
(strExample += " "),
strExample += global.DocNumAction.nCurrentDocNum, global.DocNumAction.bIncludePageNum &&
(
strExample += eval("'" + global.DocNumAction.strPageNumPrefix + "'") + ("" + (nCurPgNum + 1)), global.DocNumAction.bPageNumPostfix &&
(strExample += " of " + oOrigDoc.numPages)
);

var rcPage = oOrigDoc.getPageBox("Crop", nCurPgNum),
mxToDefaultCoords = (new Matrix2D).fromRotated(oOrigDoc, nCurPgNum),
nPgRot = oOrigDoc.getPageRotation(nCurPgNum),
rcRot = [],
nAlign,
nMargX = 72 * +global.DocNumAction.nMarginX;

/* set margins for whichever text area is being processed */
switch (global.DocNumAction.strHorzPos) {
case "PosL":
strAlign = "left",
rcRot[0] = nMargX,
rcRot[2] = nMargX + nLabWidth;
break;
case "PosC":
strAlign = "center",
rcRot[0] = rcPage[2] / 2 - nLabWidth / 2,
rcRot[2] = rcPage[2] / 2 + nLabWidth / 2;
break;
case "PosR":
strAlign = "right",
rcRot[0] = rcPage[2] - nMargX - nLabWidth,
rcRot[2] = rcPage[2] - nMargX
}
var nMargY = 72 * Number(global.DocNumAction.nMarginY),
nLines = 1,
oMtch = strExample.match(/(\n)/g);
oMtch && (nLines += oMtch.length);
var bxHght = nLines * (nLabLineHeight + 1);

/* calculate additional margin / placement information */
switch (global.DocNumAction.strVertPos) {
case "PosT":
rcRot[1] = rcPage[1] - nMargY - bxHght,
rcRot[3] = rcPage[1] - nMargY;
break;
case "PosB":
rcRot[1] = nMargY,
rcRot[3] = nMargY + bxHght
}

/* same thing for annotation */
var rectAnnot = mxToDefaultCoords.transform(rcRot),
annot = oTrgDoc.getAnnot(nPgTrgStart, "DocNumberLabel");
annot && annot.destroy(),
strExample = strExample.replace(/\r\n/g, "\r"),
oTrgDoc.addAnnot(
{
type: "FreeText",
page: nPgTrgStart,
rect: rectAnnot,
rotate: nPgRot,
width: 0,
fillColor: cBkCol,
readOnly: "Lckd" == global.DocNumAction.strBoxStateSel,
richContents: [{
textColor: ["RGB", 0, 0, 0],
textSize: nLabLineHeight,
alignment: strAlign,
text: strExample
}],
name: "DocNumberLabel"
})
}

/* if flattening pages */
if (oTrgDoc.flattenPages(),
global.DocNumAction.bSaveWPostFx) {
var cSavePath = oOrigDoc.path.replace(/\/[^\/]+$/, "/"); // may need adjustment to remove residual escaping inserted during translation / transition from older format

// KTA added this to replace "prepped" with "labeled" if using a standard tree
cSavePath = setOutputFolder(cSavePath);

/*********************************************************



var cSavePrefix = "00000" + global.DocNumAction.nCurrentDocNum.toString();
cSavePrefix = cSavePrefix.slice(-5);
cSavePath += "Exh" + cSavePrefix + "_";
*************************************************************/

// app.alert("Number of pages is " + nNumPages);
cSavePath += oOrigDoc.documentFileName.replace(/\.pdf/, ""),
"DnPr" == global.DocNumAction.strTotalPgNumInName &&
(cSavePath += " - ", cSavePath += nNumPages,
1 == nNumPages && (cSavePath += " page"),
1 != nNumPages && (cSavePath += " pages")
),
"None" == global.DocNumAction.strTotalPgNumInName,
cSavePath += ".pdf",
cSavePath = cSavePath.replace(/\,/g, ""),
oTrgDoc.saveAs(cSavePath)
}
} // end of test for whether the document has a signature
else { // document is signed and should be skipped
app.alert(event.target.documentFileName + " is signed and cannot be labeled. It will be skipped.");<--This is where I would like to insert your code in part that alerts user to signed documents. I want it to bump up the iteration. No luck so far.: if (isSigned) app.alert("This document is signed."); globaliteration++ 
}
global.iteration++; 

app.endPriv()
} // end of DoPlaceDocNumbers
) // end of label placer function declaration
} // end IF global.DocNumAction is undefined