I would prefer what the Whirlpool forums do... and just add a faint "O.P." in the top right of the post... so that it isnt in your face, but if you wanted to know who was the OP, its there for you to know [=
and example of this is here:
http://forums.whirlpool.net.au/forum-replies.cfm?t=1269051
the 1st, 3rd and 6th posts are the OP... and its just a subtle way of showing it [=