I am not sure I call this a bug, perhaps just the snippet might be wrong and this should just render a text
@v-siky-msft if you still need in the community portals this in line 12 of LoginLocal.ascx control:
<%: Html.TextSnippet("Account/SignIn/SignInLocalFormHeading", defaultValue: ResourceManager.GetString("Signin_With_Local_Account"), tagName: "span") %>
as you can see it renders using TextSnippet and not HtmlSnippet
@DouglasNLima you can achieve what you need via JavaScript
make sure you have a Content snippet called Account/SignIn/PageCopy and add your code in there, for example:
<script>
$(document).ready(function(){
$("#local-login-heading").find("span").eq(0).append("<img src='/Diagnose.png'/>");
});
</script>
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