The svg is simple and the coordinates are round numbers, so they were probably hand-written:

    <svg class='svgDiagram center' width="300" height="120" viewBox="-15 0 285 120">
      <defs>
        <g id="vector">
          <line x1="0" y1="0" x2="0" y2="45" style="stroke:#000;stroke-width:2" />
          <polygon points="0,50 -5,42 5,42" style="fill:#000;" />
        </g>
      </defs>
      <g transform='translate(100 20) rotate(0)'>
        <rect x="0" y="0" width="80" height="80" stroke='black' stroke-width='2' fill="#fff" />
        <text x="40" y="40" fill="black" text-anchor="middle" alignment-baseline="middle" font-size='28px'>m</text>
      </g>
      <use xlink:href="#vector" transform='translate(100 60) rotate(90)' />
      <text x="40" y="60" font-size='25px' text-anchor="middle" alignment-baseline="middle">F</text>
      <use xlink:href="#vector" transform='translate(180 80) rotate(-90)' />
      <text x="240" y="80" font-size='25px' text-anchor="middle" alignment-baseline="middle">F</text>
      <use xlink:href="#vector" transform='translate(180 40) rotate(-90)' />
      <text x="240" y="40" font-size='25px' text-anchor="middle" alignment-baseline="middle">F</text>
    </svg>