引导程序选择器未对齐

Question

我使用面板创建了一个小表格，但是我的选择器未与其他字段对齐。 （下图）

代码：

<div class="col-sm-6 col-sm-offset-3">
    <h3 align="center">Signature</h3>
    <div class="panel panel-default">
        <div class="panel-body">
            <div class="form-group">
                <label for="signatureName" class="col-lg-2">Signature Name:</label>
                <div class="col-lg-4">
                     <input type="text" class="form-control" name="SignatureName" id="SignatureName" />
                </div>
            </div>
            <div class="form-group">
                <label for="signatureName" class="col-lg-2">Font:</label>
                <div class="col-lg-4">
                     <select id="signatureFont" name="signatureFont" onchange="changeFont(this);" class="selectpicker">
                         <option value="">Select</option>
                         <option value="Aguafina Script">Aguafina Script</option>
                         <option value="Alex Brush">Alex Brush</option>
                         <option value="Bilbo">Bilbo</option>
                         <option value="Condiment">Condiment</option>
                         <option value="Great Vibes">Great Vibes</option>
                         <option value="Herr Von Muellerhoff">Herr Von Muellerhoff</option>
                         <option value="Kristi">Kristi</option>
                         <option value="Meddon">Meddon</option>
                         <option value="Monsieur La Doulaise">Monsieur La Doulaise</option>
                         <option value="Norican">Norican</option>
                         <option value="Parisienne">Parisienne</option>
                         <option value="Permanent Marker">Permanent Marker</option>
                         <option value="Sacramento">Sacramento</option>
                         <option value="Yellowtail">Yellowtail</option>
                    </select>
                </div>
            </div>
            <div class="form-group">
                <label for="displaySignature" class="col-lg-2">Signature:</label>
                <div class="col-lg-4">
                    <input type="text" class="form-control" name="displaySignature" id="displaySignature" readonly />
                </div>
            </div>
            <div class="form-group">
                <div class="col-lg-2">
                    <input type="button" class="btn btn-primary" value=" Sign " />
                </div>
            </div>
        </div>
    </div>
    </div>

<script>
    $(document).ready(function() {
        $('.selectpicker').selectpicker({});
    });
</script>

我应该将哪些设置应用于选择器吗？我正在为我的选择器使用bootstrap-select.min

谢谢