NASHVILLE, Tenn. -- A company already the subject of a Channel 4 I-Team investigation is now in hot water with the city over a bumper sticker.

Related: Video: Metro Legal Says Company's Ad Placement Is Defacement | Video: Customers Taken By Skydiving Gift Certificate Scheme

Some Adventure Skydiving customers were irate when they were unable to redeem expensive gift certificates they had purchased through a 1-800 number.

Now, bumper stickers advertising the company have been placed on the backs of stop signs, and Metro Legal said it will take action if the company doesn't clean up the mess.

"They've been placed on various signs," said Doug Sloan of Metro's legal department.

The brightly colored stickers have been spotted on signs around Nashville.

"It certainly is defacing public property," Sloan said.

Adventure Skydiving is the company behind 1-800-505-JUMP, run by Chuck Owen

According to the call center, Owen was in the air. He did not return Channel 4's calls.

"According to our code, it's illegal to place signs in the public right of way," Sloan said. "In particular, it's also illegal to place signs on public signs, like stop signs and telephone poles."

Sloan is also trying to reach the company.

"We'll encourage them to remove every one of the signs they've placed, and hopefully that's what they'll do," he said.

But if the company doesn't, it will face hefty fines.

"Fifty dollars per sign, per day that it remains in the public right of way," Sloan said.

Channel 4 also received an e-mail from a man who said he had one of the stickers put on his mailbox.

A change in Metro's rules allows the city to also fine the sticker makers and those posting the stickers as well.