Using font awesome it is incredibly easy to create a spinner to alert users that something is happening.

There are a number of spinner icons

enter image description here

which are easy to animate using fa-spin

<div class="fa-3x">
  <i class="fas fa-spinner fa-spin"></i>
  <i class="fas fa-circle-notch fa-spin"></i>
  <i class="fas fa-sync fa-spin"></i>
  <i class="fas fa-cog fa-spin"></i>
  <i class="fas fa-spinner fa-pulse"></i>
  <i class="fas fa-stroopwafel fa-spin"></i>
</div>