if (vAlert == false) {
        if (vMACD1 < vSignal1 && vMACD >= vSignal) {  // crossing up
            vAlert = true;
            AlertCntr += 1;
            drawShapeRelative(0, vSignal, Shape.UPARROW, null, Color.yellow, Image.TOP | Image.ONTOP, "Alert" + AlertCntr);
        }
        if (vMACD1 > vSignal1 && vMACD <= vSignal) {  // crossing down
            vAlert = true;
            AlertCntr += 1;
            drawShapeRelative(0, vSignal, Shape.DOWNARROW, null, Color.yellow, Image.BOTTOM | Image.ONTOP, "Alert" + AlertCntr);
        }
    } else {
        if ((vMACD1 < vSignal1 && vMACD < vSignal) || (vMACD1 > vSignal1 && vMACD > vSignal)) {
            vAlert = false;
            removeShape("Alert" + AlertCntr);
        }
    }
    
    return new Array(vHist, vSignal, vMACD);