DETROIT (Reuters) - Don’t blame Wall Street traders if you see them wearing cheese head hats or black and gold clothes before the National Football League’s Super Bowl championship next month.

Green Bay Packers Ryan Grant runs the ball in to score against the Pittsburgh Steelers in the fourth quarter of their NFL football game in Pittsburgh, Pennsylvania, December 20, 2009. REUTERS/ Jason Cohn

A matchup of the Pittsburgh Steelers and the Green Bay Packers in the NFL’s big game on February 6 would be a good sign -- U.S. market returns top 20 percent annually when either team plays, according to a tongue-in-cheek analysis by Capital IQ, a unit of Standard & Poor’s.

“The potentially winning combination for the markets would be a Pittsburgh Steelers and Green Bay Packers face-off,” Capital IQ said.

The average annual return for the S&P 500 index when the final game includes the Steelers, who often play in black and gold, is 25 percent, and an even better 26 percent when they win, according to the study.

Separately, the average return when the Super Bowl involves the Packers, whose fans often wear hats made to look like big blocks of cheese to celebrate Wisconsin’s dairy heritage, is 24 percent, the study said.

The markets don’t show as healthy a gain for the Chicago Bears, who will play the Packers in the NFC championship game this weekend. The market rose by about 19 percent when the team won its Super Bowl in 1986 and was up 5.5 percent after a loss in 2007, Capital IQ said.

The New York Jets, who will play the Steelers in the AFC finals this weekend, are just plain bad news as the S&P 500 fell 8 percent in 1969, according to the study.

Another bad sign is the location of the game in Dallas, as Super Bowls played in Texas average an 8 percent decline, Capital IQ said. That is the worst performance of the eight states that have hosted the NFL’s final game.

Domed stadiums, like the site of this year’s game, result in an average decline of 3 percent, the study said.

Of course, sports data can often be parsed in ways that are positive. Each of the final four teams has won the Super Bowl at least once and the average market return after a past winner is victorious again is 13 percent, the study said.

Last year’s Super Bowl, where the NFC’s New Orleans Saints defeated the Indianapolis Colts, drew a record 106.5 million American TV viewers, topping the 1983 finale of the comedy “M*A*S*H,” which drew 106 million.

While traders may take sides on Super Bowl Sunday, Capital IQ is careful not to, stating in its disclaimer that the study is not intended as a basis for investment decisions and does not represent an endorsement of any particular team.