you will have to remove your signature then copy/paste the code every time you post a message.
E.G when i post the following(spaces put into the code so you can see how it works)
__________________
[ url=http://fly.to/418squadron][img ]http://www.geocities.com/rcafhornet/hornet.txt[ /img][ /url]
[ FONT=century gothic][ B][ SIZE=3][ COLOR=darkblue]418[ /Color][ Color=red] 'Hornet'[/ color][ color=white] Squadron[ /color][ color=darkblue] RCAF[ /color][ /SIZE][/B][ /font]
it appears as below
__________________
418 'Hornet' Squadron RCAF