Before Sunday's Seattle Seahawks-San Francisco 49ers showdown, a plane flew over Candlestick Park with a "Go Hawks" banner. This was organized by a group of Hawks' fans who raised money and funded the stunt.

The 49ers won Sunday's game 19-17 and a group of 49ers' fans are planning a response...and a good one.

They have raised money via and are planning to purchase billboard space highlighting San Fran's five Super Bowl titles and also the fact that the Hawks have none. 

Here is the text from their page and their planned image:

After lots of discussion in the 49er Faithful group (and based on the great idea of Michael
Narvios), a lot of us have decided to counter the Seahawk’s plan of
flying a plane with a banner around Candlestick by placing a billboard
showing 49er pride right in Seattle, preferably by Century Link Field.

This group has been created to raise funds to place a billboard within half a mile of Century Link Field. Seahawk fans raised 2k, we can raise a lot more. We have contacted companies in Seattle with multiple billboard ad locations.
We are looking to raise about 7-8k to keep our ad there for at least 1
month, all during December and some of January for their playoff games.