To create a license plate, go to the ACME License Maker. You will need to save the image you create to your PC using the "Save Picture As" function of your browser. Your license plate will look something like this:

or

Next, upload the image file to a file sharing website, I use Image Shack. It is a free service.
Finally, paste the file sharing link “embeddable code for forums” to your signature area in your profile for this forum and save the changes.
I learned how to do this from a discussion thread at Barbecuebible.com. There is more information on how to do this there.
Jim