The SMF copyright displayed at the bottom of every SMF Forum is there for a reason. It MUST remain there, and forum administrators are NOT allowed to remove it for any reason, whatsoever. An example of a SMF copyright is:

Powered by SMF 2.0 RC3 - Revision 9824 | SMF © 2006–2010, Simple Machines LLC

The SMF license states:

a. A Modification must not alter or remove any copyright notices in the Software or Package, generated or otherwise.

Failure to comply will result in a reminder, then an official warning, followed by legal actions.