Your company will most likely show you an image and then show some HTML code underneath it. Click in the box where it shows the code you want to copy , press CTRL+A (select all) and then press CTRL+ C (copy). Then go to your forum profile and in the signature box paste the code by pressing CTRL+V (paste) . After that press submit or update - depending on your forum system- and then post something to make sure it shows up right.
I'm positive that this will work 100%. If it doesn't work check to see if the signature allows HTML code.