The sig rules are fairly flexible and comprise of a 120x60 button with three lines of an unaltered normal text font PROVIDING you have a reciprocal banner on your sites pointing back to Oprano.
Sponsors have a lot more flexibility and if you wish to fly a 468x60 banner in your sig I suggest you talk to The Enforcer or contact him on
advertising@oprano.com, who can also supply you with a link for the oprano buttons/banners should you require.