[IdanB]

open admincp, specific the style you wish to change.
There should be 2 templates:
"postbit" & "postbit_legacy".
In it, look for this block:

PHP Code:

<if condition="$post['signature']">
        <!-- sig -->
            <div>
                __________________<br />
                $post[signature]
            </div>
        <!-- / sig -->
        </if> 


and replace with:

PHP Code:

<if condition="$post['signature']">
        <!-- sig -->
            <div align="center">
                __________________<br />
                $post[signature]
            </div>
        <!-- / sig -->
        </if>