very simple tick formatter

A small exampe of how you can make your tick labels display as you'd like them to.

note D3 can provide its own formatter fuctions for common cases here

<html>
<head>
	<title>tick format example</title>
	<style type="text/css">
		svg{font-family: sans-serif;}
		.domain{fill:none; stroke:#000;}
		.tick, line{stroke:#000;}
		.tick, text{stroke:none;}
	</style>
</head>

</body>
<script type="text/javascript">
//make a scale
var xScale = d3.scale.linear()
	.range([0, 500])
	.domain([-0.5, 0.5]);

//make an axis
var myAxis = d3.svg.axis()
	.scale( xScale ) //based on the scale we just made
	.tickFormat(neatDecimal);   //give it a tickFormat, a function which tells the scale how to display the tick values

function neatDecimal(number){
	if(number == 0){ //if the number is zero, return it without any decimal places
		return 'O';  //i've changed it to an 'O'
	}
	//otherwise just leave it as is
	return number;
}

//then lets attach it to the page...

d3.select('body')
	.append('svg').attr({height:100, width:700}).append('g').attr('transform','translate(100,0)')
	.call(myAxis)
</script>
</html>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js