Wanted to make a seperate post so as to not confuse people too much. I have just made the following changes to my site and thus aligned signatures to the bottom where they should be.
OPEN viewtopic_body.tpl || I am using acidtech so apologies if this differs from your theme.
FIND
[code]<BEGIN><BEGIN><tbody id="post_{postrow.POST_ID}" style="display]
REPLACE WITH
[code]<BEGIN><BEGIN><tbody id="post_{postrow.POST_ID}" style="display]
Basically the signature was being tagged onto a table that would dynamically resize to suit post length. I have added a new table cell at the bottom and included signature there thus always having it at the bottom.
This is all subject to testing so please feel free to post back thoughts/ outcomes.