https://github.com/szimek/signature_pad

Code to make signature work:

<script src="https://cdnjs.cloudflare.com/ajax/libs/signature_pad/4.1.5/signature_pad.js"></script>

<div class="col-sm-8">
	<canvas id="signature-pad" width="400" height="200"></canvas>
	<button id="clear-button">Clear</button>
</div>

<style>
	#signature-pad {
		border: 1px solid #000;
	}
</style>
<script>
	// Initialize Signature Pad
	var canvas = document.getElementById('signature-pad');
	var signaturePad = new SignaturePad(canvas);

	// Clear button event handler
	var clearButton = document.getElementById('clear-button');

	clearButton.addEventListener('click', function () {
		signaturePad.clear();
	});

	function getSignatureData() {
		//var canvas = document.getElementById('signature-pad');
		//var signaturePad = new SignaturePad(canvas);
		if (signaturePad.isEmpty()) {
			return 'error';
		}
		var signatureData = signaturePad.toDataURL();
		return signatureData;
	}
</script>