bootstrap-icons/icons/octagon.svg

<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="currentColor" class="bi bi-octagon" viewBox="0 0 16 16">
  <path d="M4.54.146A.5.5 0 0 1 4.893 0h6.214a.5.5 0 0 1 .353.146l4.394 4.394a.5.5 0 0 1 .146.353v6.214a.5.5 0 0 1-.146.353l-4.394 4.394a.5.5 0 0 1-.353.146H4.893a.5.5 0 0 1-.353-.146L.146 11.46A.5.5 0 0 1 0 11.107V4.893a.5.5 0 0 1 .146-.353zM5.1 1 1 5.1v5.8L5.1 15h5.8l4.1-4.1V5.1L10.9 1z"/>
</svg>