All Octicons
alert-fill
Octicon sizes navigation
React
import {AlertFillIcon} from '@primer/octicons-react' <AlertFillIcon size={12} />
Rails
<%= render(Primer::Beta::Octicon.new(:"alert-fill", size: :xsmall)) %>
Jekyll
{% octicon alert-fill height:12 %}
Figma
This icon is called alert-fill-12
in Primer's Octicons library.