Endorse cars. Look at Eminem and Chrysler.

Endorse candidates. Look at what Oprah did for Obama.

Endorse Chop-O-Matics and Pocket Fishermen. Look at what Ron Popeil did for himself and the fortune he made.

But endorse porn? That does not exactly improve one’s stature in the community.

The National Football League knows that, and league attorneys are investigating an advertisement for a porn industry event that apparently featured unlicensed images of NFL players. The players were pictured in uniform for an advertisement for the Exxxotica Expo 2011, which was held in Miami last month.

"The NFL office works on behalf of the clubs to protect their intellectual property rights in matters such as this," said NFL spokesman Brian McCarthy.

The ad features Kansas City Chiefs cornerback Brandon Flowers and safety Eric Berry, Chicago Bears safety Major Wright, Houston Texans cornerback Kareem Jackson and Oakland Raiders wide receiver Jacoby Ford. It bills them as “hosts” of the event, along with three NFL rookies.

Wright, who played for the University of Florida, distanced himself from the event via his Twitter account, writing, "FYI..... I have NOTHING to do with the Exotic Expo @ the Rosemont! My pic was used without my permission. No Affiliation at all."

In response to inquiries on Twitter, Ford responded that he was not present at the event, adding he was not even in Miami when it took place.

Flowers and Jackson have not commented.

Exxxotica Expo 2011, which bills itself as the world's largest gathering of porn stars, is set to open next month in suburban Chicago.

I know five NFL players who will probably stay a long way away from the Windy City in July.