A searchable guide to the complete WordPress Icon Library (@wordpress/icons) package from Gutenberg.
import { Icon, formatUnderline } from '@wordpress/icons';
<Icon icon={formatUnderline} />
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" aria-hidden="true" focusable="false"><path d="M7 18v1h10v-1H7zm5-2c1.5 0 2.6-.4 3.4-1.2.8-.8 1.1-2 1.1-3.5V5H15v5.8c0 1.2-.2 2.1-.6 2.8-.4.7-1.2 1-2.4 1s-2-.3-2.4-1c-.4-.7-.6-1.6-.6-2.8V5H7.5v6.2c0 1.5.4 2.7 1.1 3.5.8.9 1.9 1.3 3.4 1.3z"></path></svg>
formatUnderline – WordPress Icon Library