Maybe someone will be useful this option without the plugin.
Go to templates > forums > front > topics > post
find
<div class='cPost_contentWrap ipsPad'>
after adding
{{if $comment->author()->member_id and $item->author()->member_id == $comment->author()->member_id}}
<div style="margin-top:-8px; margin-right:0px; position:absolute;z-index:100;" class="SVG ipsResponsive_hidePhone">
<div class="ipsResponsive_hidePhone">Автор темы</div></div>{{endif}}
in custom.css
.SVG {
position: absolute;
font-size: 15px;
z-index: 5;
height: 25px;
font-weight: 400;
font-family: "Bebas Neue", sans-serif;
text-align: center;
line-height: 25px;
right: -6px;
top: 10px;
color: #3e4148;
border-top-right-radius: 3px;
border-top-left-radius: 3px;
border-bottom-left-radius: 3px;
background-color: #d4202763;
text-shadow: 0px 0.03em 0px rgba(0, 0, 0, 0.1), 0px 0.15em 0.11em rgba(0, 0, 0, 0.1), 0px 0.25em 0.02em rgba(0, 0, 0, 0.05), 0px 0.32em 0.32em rgba(0, 0, 0, 0.05);
box-shadow: 0px 0.03em 0px rgba(0, 0, 0, 0.2), 0px 0.15em 0.11em rgba(0, 0, 0, 0.04), 0px 0.25em 0.02em rgba(0, 0, 0, 0.04), 0px 0.32em 0.32em rgba(0, 0, 0, 0.04);
width: 10%;
-webkit-backface-visibility: hidden;
-moz-backface-visibility: hidden;
backface-visibility: hidden;
}
.SVG:before {
clear: both;
display: block;
}
.SVG:after {
content: '';
position: absolute;
border-right: 6px solid transparent;
border-bottom: 0;
border-top: 8px solid #d4202763;
border-left: 0t;
right: 0;
bottom: -8px;
z-index: 1;
}