I do something similar on my website to denote links that open in a new tab (which I use to denote "external" links). I use an SVG icon, though this is less accessible than some of the other comments I'm seeing here.

:is(.post-content, section#comments) a[target="_blank"]:not(.no-arrow)::after {
    content: ' ';
    background-color: currentColor;
    mask-image: url("data:image/svg+xml;base64,...");
    margin: 0 0 0 0.25em;
    width: calc(min(1em, 8px));
    height: calc(min(1em, 8px));
    display: inline-block;
}