I don't like to use <span> at all... many times it seems better to use the own <div>. Usually, in vBulletin at least, you can add/edit that for each usergroup.

Well, come on see the "opening" tag and its end. And the CSS used in there, as we can see it is:

* For all usergroups
Code: 
.usergroup1, .usergroup2, .usergroup3
{
color:#fff;
background:#65a830;
padding:3px 8px;
font-size:11px;
-moz-border-radius:3px;
-webkit-border-radius:3px  #fff;
border-radius:3px #fff;
margin-bottom:2px;
display:inline-block
}
* For custom one usergroup
Code: 
.usergroup1
{
background:#FDD017
}
So, if you put it in your main CSS style... you can easily set in your forum settings to rule the tag:

Code: 
<div class="usergroup1"></div>
I hope helped you!

* EDIT: I DIDN'T SEE THE OTHER REPLY FOR THAT. THIS IS OTHER ONE ANYWAY. THANK YOU.