By default, vB5's signatures do not have a dividing line to separate them from the post they are under.
On longer posts this can make it difficult for users to distinguish where the post ends and the signature starts.
To add a dividing line that matches the general styling, add this to the template css_additional.css:
.post-signature { border-top: 1px dotted {vb:stylevar post_controls_divider_color}; margin-top: 0px; padding-top: 15px; }
AdminCP > Settings > Options > Topic Display Options (showthread) > Post Signature Inline
Make sure this option is set to "Yes", if not, change it and save.