And it is quite easy if you find one you would like to be a BBcode you can ask for it to be created for the site. Quite easy for it to be ratified if actually a worthwhile adventure to create it.
Just remember that some sites may have certain BBcodes turned off.
Ex. I know a site that HATES having multiple colors in posts so they made every color be a green color. Some sites have no colors possible.
So it varies from site to site.