How to have custom marker symbol(‘[‘ and ‘]’) in Plotly.js

I’m working on a project that requires graphs. I’m using Plotly with JS.

I want custom symbols ‘[‘ or ‘]’ as markers on the graph.
Although i prefer without usage of svg, I’m open to change.
How?

I tried:
HTML Code:

index.html

<!DOCTYPE html>
<html>
<head>
    <title>Graphs</title>
    <script src="https://cdn.plot.ly/plotly-latest.min.js"></script>
</head>
<body>
    <div id="graph-1"></div>
    <script src="index.js"></script>
</body>
</html>

JS Code:

index.js

graph_1_data = [{
    x: [1, 2, 3],
    y: [1, 2, 3],
    mode: 'lines+markers',
    line: {
        shape: 'linear',
        color: 'blue'
    },
    marker: { 
        symbol: "[", #Here even though I give '[' it's showing circle[it's default probably] on the plotted graph
        size: 15
    }
}]
graph_1_layout = {
    title: "Graph-1"
}
Plotly.newPlot('graph-1',graph_1_data, graph_1_layout);

Please help me get Custom Markers(‘[‘ and ‘]’ to be specific) in Plotly JS