metamask-extension/app/images/alert-red.svg

<svg height="16" width="16" xmlns="http://www.w3.org/2000/svg">
    <g fill="none" fill-rule="evenodd">
        <circle cx="8" cy="8" fill="#d0021b" r="8"/>
        <g fill="#fff">
            <rect height="7" rx="1" width="2" x="7" y="3"/>
            <rect height="2" rx="1" width="2" x="7" y="11"/>
        </g>
    </g>
</svg>