How do I append HTML after a form title?
You shouldn't concatenate the result of the t() function, it should rather be built up as a single string:

'#title' =&gt; t('Name &lt;span&gt;!&lt;/span&gt;'),


Other than that, you're already doing this about the cleanest way possible. Other approaches would involve post-processing the form element(s) to render their title in a different way than standard. I imagine that would end up being more trouble than it's worth unless you wanted to do it globally for every element in every form in the site.